Main Board for Omega Home Computer
The main board implements standard MSX2* functionality, as described in the Specifications section below. The main board is designed to be stacked under the keyboard PCB, thus creating a "keyboard computer" form factor typical for 1980's home computers.
- Processor: Zilog Z80 CPU (CMOS version - Z84C00) running at 3.58 MHz
- Memory:
- RAM: 512 KiB SRAM, expandable to 4 MiB using an optional daugherboard. MSX* compatible memory pager. The RAM is mapped to slot 3-2
- ROM: 256 KiB or 512 KiB Flash ROM. The ROM is mapped to the slot 0 and sub slots 3-0, 3-1, and 3-3
- Video: Yamaha V9958 or Yamaha V9938 VDP
- 128 KiB Video RAM
- Composite, S-Video, and RGB video outputs
- Audio: Yamaha YM2149 or General Instrument AY-3-8910 PSG
- Two MSX* compatible cartridge slots
- Keyboard, joysticks, printer and cassette recorder interfaces
- RTC: Ricoh RP5C01
- Microprocessor Supervisor:
- Reset generation
- RTC battery backup
- BIOS: C-BIOS. Compatible with BIOSes from the original MSX2* computers with a similar slot organization and hardware specifications, for example Sanyo* PHC-23J
Connect regulated +5V power supply to this connector.
Note: On-board components use only 5V supply voltage. Some cartridges might also need 12V/-12V supply voltage. J10 connector should be used in this case.
| Pin | Description |
|---|---|
| Tip (the inner contact) | Power: 5V (positive terminal) |
| Barrel / Sleeve | Power: GND (negative terminal) |
| Pin | Description |
|---|---|
| Tip (the inner contact) | Output: Composite Video |
| Ring / Sleeve | Power: GND |
| Pin | Description |
|---|---|
| Tip (the inner contact) | Output: Audio (line level) |
| Ring / Sleeve | Power: GND |
| Pin | Description |
|---|---|
| 1, 2 | Power: GND |
| 3 | Output: Luminance (intensity) |
| 4 | Output: Chrominance (color) |
| Pin | Description |
|---|---|
| 1 | Power: GND |
| 2 | Output: Audio (line level) |
| 3 | Output: AV (4.55V) |
| 4 | Output: Composite Video |
| 5 | Output: YS (3 V) |
| 6 | Output: Red |
| 7 | Output: Green |
| 8 | Output: Blue |
| Pin | Description |
|---|---|
| 1, 2, 3, 8 | Power: GND |
| 4 | Output: Sound output to cassette recorder (microphone level) |
| 5 | Input: Sound input from cassette recorder (line level) |
| 6 | Output: Relay - Motor control |
| 7 | Output: Relay - Motor control |
| Pin | Description |
|---|---|
| 1 | Input: Forward (north / up) |
| 2 | Input: Backward (south / down) |
| 3 | Input: Left (west) |
| 4 | Input: Right (east) |
| 5 | Power: 5V |
| 6 | Input: Trigger 1 |
| 7 | Input: Trigger 2 |
| 8 | Output: Joystick select |
| 9 | Power: GND |
| Pin | Description |
|---|---|
| 1 | Output: /STROBE |
| 2 | Output: D0 |
| 3 | Output: D1 |
| 4 | Output: D2 |
| 5 | Output: D3 |
| 6 | Output: D4 |
| 7 | Output: D5 |
| 8 | Output: D6 |
| 9 | Output: D7 |
| 10 | No connection |
| 11 | Input: Busy |
| 12 | No connection |
| 13 | No connection |
| 14 | Power: GND |
Connect regulated 5V/12V/-12V power supply to this connector.
| Pin | Description |
|---|---|
| 1, 2, 3 | Power: GND |
| 4, 5, 6 | Power: 5V |
| 7 | Power: 12V |
| 8 | Power: -12V |
| Pin | Description | Pin | Description |
|---|---|---|---|
| 1 | Input: Column 0 | 2 | Power: 5V |
| 3 | Input: Column 1 | 4 | Output: Row A |
| 5 | Input: Column 2 | 6 | Output: Row B |
| 7 | Input: Column 3 | 8 | Output: Row C |
| 9 | Input: Column 4 | 10 | Output: Row D |
| 11 | Input: Column 5 | 12 | Output: Caps Lock LED |
| 13 | Input: Column 6 | 14 | Output: Kana LED |
| 15 | Input: Column 7 | 16 | Power: GND |
| Pin | Description | Pin | Description |
|---|---|---|---|
| 1 | Power: 5V | 2 | Power: 5V |
| 3 | Output: /RAM2_CS | 4 | Output: /RAM1_CS |
| 5 | Output: /RAM4_CS | 6 | Output: /RAM3_CS |
| 7 | Output: /RAM6_CS | 8 | Output: /RAM5_CS |
| 9 | Output: RAM_A18 | 10 | Output: /RAM7_CS |
| 11 | Output: RAM_A16 | 12 | Output: RAM_A15 |
| 13 | Output: RAM_A14 | 14 | Output: RAM_A17 |
| 15 | Output: A12 | 16 | Output: /WR |
| 17 | Output: A7 | 18 | Output: A13 |
| 19 | Output: A6 | 20 | Output: A8 |
| 21 | Output: A5 | 22 | Output: A9 |
| 23 | Output: A4 | 24 | Output: A11 |
| 25 | Output: A3 | 26 | Output: /RD |
| 27 | Output: A2 | 28 | Output: A10 |
| 29 | Output: A1 | 30 | Bi-directional: MD7 |
| 31 | Output: A0 | 32 | Bi-directional: MD6 |
| 33 | Bi-directional: MD0 | 34 | Bi-directional: MD5 |
| 35 | Bi-directional: MD1 | 36 | Bi-directional: MD4 |
| 37 | Bi-directional: MD2 | 38 | Bi-directional: MD3 |
| 39 | Power: GND | 40 | Power: GND |
| Pin | Description | Pin | Description |
|---|---|---|---|
| 1 | In/Out: /RESET | 2 | Power: GND |
| 3 | Input: /NMI | 4 | Power: GND |
| Pin | Description |
|---|---|
| 1 | Power: 5V |
| 2 | Output: /DHCLK |
| 3 | Output: /DLCLK |
| 4 | Output: CBDR |
| 5 | In/Out: CB7 |
| 6 | In/Out: CB6 |
| 7 | In/Out: CB5 |
| 8 | In/Out: CB4 |
| 9 | In/Out: CB3 |
| 10 | In/Out: CB2 |
| 11 | In/Out: CB1 |
| 12 | In/Out: CB0 |
| 13 | Power: GND |
JP1 selects whether bottom 256 KiB or top 256 KiB of 512 KiB Flash ROM are mapped to the system memory / slots.
| Jumper Position | Description |
|---|---|
| Open* | Use Flash ROM addresses 0x00000 - 0x3FFFF |
| Closed | Use Flash ROM addresses 0x40000 - 0x7FFFF |
JP2 selects the layout for Japanese keyboards
| Jumper Position | Description |
|---|---|
| Open* | JIS layout |
| Closed | ANSI/AIUEO/50on layout |
JP3 and JP4 select VDP type used. JP3 connects VDP pin 21 either to 470 ohm pull-up (V9938, unused composite video output), or to 5V power supply (V9958, DAC power supply). JP4 selects whether VDP CSYNC output goes directly to RGB encoder (V9958) or to a level shifer circuit (V9938).
Warning: Incorrect setting of JP3 will damage VDP
| Jumper Position | Description |
|---|---|
| 1-2 | V9938 VDP |
| 2-3 | V9958 VDP |
JP5 and JP6 selects the color encoding system for the video output. More specifically, JP5 configures the RGB encoder and JP6 selects the color subcarrier frequency.
Note: Some components used only for PAL color subcarrier frequency generation, and can be omitted if NTSC color encoding is used. Refer to Bill of Materials section for more information
| Jumper Position | Description |
|---|---|
| 1-2 | NTSC |
| 2-3 | PAL |
Omega Mainboard project on Mouser.com - View and order all components except of the PCB, Yamaha V9958 VDP, Yamaha YM2149 PSG, Ricoh RP5C01 RTC, NEC D41464 DRAM, Sony CXA1645P RGB Encoder, and CR2032 battery.
| Component type | Reference | Description | Quantity | Possible sources and notes |
|---|---|---|---|---|
| PCB | Omega Mainboard PCB - Version 1.1 | 1 | Refer to the RetroBrew Computers Board Inventory page for ordering information, or order from a PCB manufacturer of your choice using provided Gerber or KiCad files | |
| Integrated Circuit | U1 | Z80 CPU, CMOS, 40 pin DIP - Z84C00xxPEG | 1 | Mouser 692-Z84C0010PEG |
| Integrated Circuit | U2 | 82C55 PPI, CMOS, 40 pin DIP - CP82C55AZ | 1 | Mouser 968-CP82C55A-5Z |
| Integrated Circuit | U3 | V9958 VDP, 64 pin DIP | 1 | eBay. Note: V9938 VDP can be used instead |
| Integrated Circuit | U4 | YM2149 PSG, 40 pin DIP or AY-3-8910 | 1 | eBay |
| Integrated Circuit | U5 | RP5C01 RTC, 18 pin DIP | 1 | eBay |
| Integrated Circuit | U6 | 512 KiB Flash ROM, 32 pin DIP - SST39SF040 | 1 | Mouser 804-39SF0407CPHE |
| Integrated Circuit | U7 | 512 KiB SRAM, 32 pin DIP - AS6C4008 | 1 | Mouser 913-AS6C4008-55PCN |
| Integrated Circuit | U8 - U11 | D41464, 64K x 4 DRAM, 18 pin DIP | 4 | eBay |
| Integrated Circuit | U12 - U14 | Simple Programmable Logic Device - ATF16V8B | 3 | Mouser 556-AF16V8B15PU |
| Integrated Circuit | U15 - U18 | 4-by-4 Register File - 74HC670, 16 pin DIP | 4 | Mouser 595-CD74HC670E |
| Integrated Circuit | U19 - U21 | 74F541, 20 pin DIP | 3 | Mouser 595-SN74F541N |
| Integrated Circuit | U22 | 74HCT540, 20 pin DIP | 1 | Mouser 595-SN74HCT540N |
| Integrated Circuit | U23, U24 | 74HCT273, 20 pin DIP | 2 | Mouser 595-SN74HCT273N. Note U24 is optional - printer port support. |
| Integrated Circuit | U25, U26 | 74F245, 20 pin DIP | 2 | Mouser 595-SN74F245N |
| Integrated Circuit | U27 | 74HCT175, 16 pin DIP | 1 | Mouser 595-CD74HCT175E |
| Integrated Circuit | U28, U29 | 74HCT157, 16 pin DIP | 2 | Mouser 595-SN74HCT157N |
| Integrated Circuit | U30, U31 | 74HCT153, 16 pin DIP | 2 | Mouser 595-CD74HCT153E |
| Integrated Circuit | U32 | 74AHCT138, 16 pin DIP | 1 | Mouser 595-SN74AHCT138N |
| Integrated Circuit | U33 | 74AHCT125, 14 pin DIP | 1 | Mouser 595-SN74AHCT125N. Note U33 is optional - printer port support. |
| Integrated Circuit | U34 - U36 | Dual Flip Flop - 74HCT74, 14 pin DIP | 3 | Mouser 595-SN74HCT74N |
| Integrated Circuit | U37 - U39 | 74AHCT32, 14 pin DIP | 3 | Mouser 595-SN74AHCT32N |
| Integrated Circuit | U40, U41 | 74HCT30, 14 pin DIP | 2 | Mouser 595-CD74HCT30E |
| Integrated Circuit | U42 | 74LS07, 14 pin DIP | 1 | Mouser 595-SN74LS07N |
| Integrated Circuit | U43 | 74HCT04, 14 pin DIP | 1 | Mouser 595-SN74HCT04N |
| Integrated Circuit | U44 | 74AHCT02, 14 pin DIP | 1 | Mouser 595-SN74AHCT02N |
| Integrated Circuit | U45 | 74HCT00, 14 pin DIP | 1 | Mouser 595-SN74HCT00N |
| Integrated Circuit | U46 | Microprocessor Supervisory Circuit - ADM691A | 1 | Mouser 584-ADM691AANZ; Possible alternatives: MAX691, LTC691, ADM691 |
| Integrated Circuit | U47 | Sony CXA1645P RGB Encoder, 24 pin DIP-400 | 1 | eBay |
| Integrated Circuit | U48 | MCP6281-E/P Operational Amplifier, 8 pin DIP | 1 | Mouser 579-MCP6281-E-P |
| Integrated Circuit | U49 | LM311N, Voltage Comparator, 8 pin DIP | 1 | Mouser 926-LM311N-NOPB. Note U49 is optional - cassette recorder support. |
| Capacitor | C1 - C58 | 0.1 uF, MLCC, 5 mm Pitch | 58 | Mouser 594-K104K15X7RF53H5 |
| Capacitor | C59 - C64 | 220 uF, Electrolytic | 6 | Mouser 647-UBW1E221MPD. Note C62 - C64 optional - RGB output support |
| Capacitor | C65 - C67 | 100 uF, 16V, Aluminum Organic Polymer | 3 | Mouser 80-A750EK107M1CAAE18 |
| Capacitor | C68 - C70 | 10 uF, MLCC, 5 mm Pitch | 3 | Mouser 810-FG28X5R1E106MR00. Note C71 optional - cassette recorder support. |
| Capacitor | C71 - C77 | 10 uF, Electrolytic | 7 | Mouser 647-UPW1E100MDD1TD. Note C71 optional - cassette recorder support. |
| Capacitor | C78 | 1 uF, Electrolytic | 1 | Mouser 710-860020672005. Note C78 optional - cassette recorder support. |
| Capacitor | C79, C80 | 22 nF, MLCC, 5 mm Pitch | 2 | Mouser 810-FG28X7R1H223KNT0. Note C79, C80 optional - cassette recorder support. |
| Capacitor | C81 | 1.5 nF, MLCC, 5 mm Pitch | 1 | Mouser 810-FG28C0G1H152JNT0 |
| Capacitor | C82 - C84 | 330 pF, MLCC, 5 mm Pitch | 3 | Mouser 810-FG28C0G1H331JNT0 |
| Capacitor | C85 | 47 pF, MLCC, 5 mm Pitch | 1 | Mouser 810-FG28C0G1H470JNT0 |
| Capacitor | C86, C87 | 33 pF, MLCC, 5 mm Pitch | 2 | Mouser 810-FG28C0G1H330JNT0 |
| Capacitor | C88 - C90 | 30 pF, Trim Capactiors, 5 mm Pitch | 3 | Mouser 659-GKG30015. Note: Can be replaced with Mouser 810-FG28C0G2A270JNT0 if color subcarrier frequency tunning is not required. DigiKey 2447-GKG30015-ND (Mouser doesn't stock them anymore). |
| Capacitor | C91 | 27 pF, MLCC, 5 mm Pitch | 1 | Mouser 810-FG28C0G2A270JNT0. Note C91 should be 18 pF for PAL support. |
| Capacitor | C92, C93 | 22 pF, MLCC, 5 mm Pitch | 2 | Mouser 810-FG28C0G1H220JNT0 |
| Capacitor | C94 | 4.7 pF, MLCC, 5 mm Pitch | 1 | Mouser 810-FG28C0G1H4R7CNT0 |
| Resistor Array | RR1 - RR4 | 10 kohm, bussed, 10 pin SIP | 4 | Mouser 652-4610X-1LF-10K or Mouser 652-4610X-AP1-103LF |
| Resistor Array | RR5 - RR7 | 4.7 kohm, bussed, 10 pin SIP | 3 | Mouser 652-4610X-1LF-4.7K or Mouser 652-4610X-AP1-472LF |
| Resistor Array | RR8, RR10 | 4.7 kohm, bussed, 6 pin SIP | 1 (2) | Mouser 652-4606X-1LF-4.7K or Mouser 652-4606X-AP1-472LF. Note RR10 is optional - Memory pager size workaround. |
| Resistor Array | RR9 | 470 ohm, bussed, 6 pin SIP | 1 | Mouser 652-4606X-1LF-470 or Mouser 652-4606X-AP1-471LF |
| Resistor | R1 | 1 Mohm, axial | 1 | Mouser 603-MFR-25FBF52-1M. Note R1 is optional - PAL support. |
| Resistor | R2, R3 | 470 kohm, axial | 2 | Mouser 603-MFR-25FBF52-470K |
| Resistor | R4 | 220 kohm, axial | 1 | Mouser 603-MFR-25FBF52-220K |
| Resistor | R5, R6 | 100 kohm, axial | 2 | Mouser 603-MFR-25FBF52-100K |
| Resistor | R7, R8 | 47 kohm, axial | 2 | Mouser 603-MFR-25FBF52-47K |
| Resistor | R9, R10 | 20 kohm, 1% tolerance, axial | 2 | Mouser 603-MFR-25FBF52-20K. Note R9 should be 16 kohm, 1% for PAL support. |
| Resistor | R11 - R14 | 10 kohm, axial | 4 | Mouser 603-MFR-25FBF52-10K. Note R11, R12 are optional - cassette recorder support. Note R14 is optional - RGB output support. |
| Resistor | R15 | 5.6 kohm, axial | 1 | Mouser 603-MFR-25FBF52-5K6 |
| Resistor | R16 - R22 | 4.7 kohm, axial | 7 | Mouser 603-MFR-25FBF52-4K7. Note R18 - R20 are optional - cassette recorder support. |
| Resistor | R23, R24 | 2.7 kohm, axial | 2 | Mouser 603-MFR-25FBF52-2K7. Note R23, R24 are optional - cassette recorder support. |
| Resistor | R25, R26 | 2.2 kohm, axial | 2 | Mouser 603-MFR-25FBF52-2K2 |
| Resistor | R27 - R33 | 1 kohm, axial | 7 | Mouser 603-MFR-25FBF52-1K. Note R31, R32 are optional - cassette recorder support. Note R33 is optional - RGB output support. |
| Resistor | R34 | 470 ohm, axial | 1 | Mouser 603-MFR-25FBF52-470R |
| Resistor | R35 | 180 ohm, axial | 1 | Mouser 603-MFR-25FBF52-180R. Note R35 is optional - RGB output support. |
| Resistor | R36 | 120 ohm, axial | 1 | Mouser 603-MFR-25FBF52-120R. Note R36 is optional - RGB output support. |
| Resistor | R37 - R42 | 100 ohm, axial | 6 | Mouser 603-MFR-25FBF52-100R. Note R42 is optional - cassette recorder support. |
| Resistor | R43 - R48 | 75 ohm, axial | 6 | Mouser 603-MFR-25FBF52-75R. Note R46 - R48 are optional - RGB output support. |
| Relay | RY1 | 5V SPDT relay | 1 | Mouser 653-G5V-1-DC5 or Mouser 653-G5V-1-T90-DC5 |
| Inductor | L1 | 68 uH, axial | 1 | Mouser 542-78F680-RC |
| Inductor | L2, L3 | 5.6 uH, axial | 2 | Mouser 542-78F5R6J-RC |
| Diode | D1 | 1N4148 | 1 | Mouser 512-1N4148TR. Note D1 is optional - cassette recorder support. |
| Transistor | Q1, Q2 | PN2907A | 2 | Mouser 512-PN2907ATF. Note Q1 is optional - cassette recorder support; Q2 is required for V9938 VDP only |
| Crystal | Y1 | 21.477270 MHz | 1 | Mouser 695-HC49US-214-U |
| Crystal | Y2 | 32768 Hz | 1 | Mouser 815-AB38T-32.768KHZ |
| Crystal | Y3 | 4.433618 MHz | 1 | Mouser 520-HCU443-20X. Note Y3 is optional - PAL support. |
| Polyfuse | F1 | 750 mA, radial, 5 mm pitch | 1 | Mouser 650-RUSBF075-2 |
| Connector | J1 | DC Power Jack, 2mm | 1 | Mouser 806-KLDX-0202-A |
| Connector | J2 | RCA Phono connector, Yellow | 1 | Mouser 490-RCJ-014 |
| Connector | J2 | RCA Phono connector, White | 1 | Mouser 490-RCJ-013 |
| Connector | J4 | Mini DIN 4-pos, Right Angle, PCB mount | 1 | Mouser 490-MD-40SM |
| Connector | J5, J6 | DIN 8-pos, Right Angle, PCB mount | 2 | Mouser 490-SDF-80J. Note J5 is optional - RGB support; J6 is optional - cassette recorder support. |
| Connector | J7, J8 | Sub-D DE9M, Right Angle, PCB mount | 2 | Mouser 523-L717SDE09P1ACH3R |
| Connector | J9 | Micro Ribbon 14-pos, Female, Right Angle, PCB mount | 1 | Mouser 636-112-014-213R001. Note J9 is optional - printer port support. |
| Connector | J10 | 8 pin friction lock connector | 1 | Mouser 571-6404568 |
| Connector | J11 | 2x8 pin header, shrouded | 1 | Mouser 710-61201621621 |
| Connector | J12 | 2x20 pin socket | 1 | Mouser 517-929852-01-20-RB |
| Connector | J13 | 2x2 pin header | 1 | Note: Optional /RESET and /NMI header |
| Connector | J14 | 1x13 pin header | 1 | Note: Optional Color Bus header |
| Connector | SLOT1, SLOT2 | 50 pin card edge connector | 2 | Mouser 571-5530843-5 |
| Jumper | JP1, JP2 | 2 pin header | 2 | Mouser 649-78229-102HLF |
| Jumper | JP3 - JP6 | Wire link | 4 | Wire link |
| Jumper | JP7, JP8 | 2x3 pin header | 0 (2) | Note JP7 and JP8 are optional - Memory pager size workaround. |
| Battery Holder | BT1 | CR2032 Battery holder | 1 | Mouser 122-2420-GR |
| Battery | BT1 | CR2032 Battery | 1 | Mouser 614-CR2032-200, 658-CR2032. Note: Not included in Mouser Project due to shipping restrictions. |
| IC Socket | U1, U2, U4 | 40 pin DIP | 3 | Mouser 517-4840-6000-CP |
| IC Socket | U3 | 64 pin DIP | 1 | eBay |
| IC Socket | U3 | 64 pin DIP (alternate) | 1 | DigiKey 117-87-764-41-005101 |
| IC Socket | U3 | 64 pin DIP (pin strips, alternate) | 4 | DigiKey 317-87-121-41-005101 |
| IC Socket | U6, U7 | 32 pin DIP | 2 | Mouser 517-4832-6000-CP |
| IC Socket | U47 | 24 pin DIP, 400 mil spacing | 1 | Mouser 517-4824-6000-CP or 517-4824-3000-CP. Note: Cut the socket in the middle. If using a socket with 600 mil spacing, remove excess material. Alternatively, solder U47 (CXA1645P) without using a socket. |
| IC Socket | U47 | 24 pin DIP, 400 mil spacing (alternate) | 1 | DigiKey 110-93-424-41-001000 |
| IC Socket | U12 - U14, U19 - U26 | 20 pin DIP | 11 | Mouser 517-4820-3000-CP |
| IC Socket | U5, U8 - U11 | 18 pin DIP | 5 | Mouser 517-4818-3000-CP |
| IC Socket | U15 - U18, U27 - U32, U46 | 16 pin DIP | 11 | Mouser 517-4816-3000-CP |
| IC Socket | U33 - U45 | 14 pin DIP | 13 | Mouser 517-4814-3000-CP |
| IC Socket | U48, U49 | 8 pin DIP | 2 | Mouser 517-4808-3000-CP |
The Omega Main Board can be configured to support either NTSC (60 Hz) or PAL (50 Hz) video standard. To support NTSC standard the board should be configured as follows:
- Install a wire links JP5 and JP6 in 1-2 position for NTSC standard support
- Do not install the following components, they are required for PAL support only:
- Crystal Oscillator: Y3
- Capacitors: C90, C93
- Resistors: R1, R30
- If using V9958 VDP also do not install the following components:
- Capacitor: C43
- Integrated Circuit: U43
- If using V9938 VDP do install the following components, they are used for V9938 VDP CSYNC level converter:
- Capacitor: C43
- Integrated Circuit: U43
- Install a wire link instead of C93 to avoid floating inputs on U43
To support PAL standard the board should be configured as follows:
- Install a wire links JP5 and JP6 in 2-3 position for PAL standard support
- Install the following components:
- Crystal Oscillator: Y3
- Capacitors: C43, C90, C93
- Resistors: R1, R30
- Integrated Circuits: U43
- Replace the following components:
- R9 use 16 kohm resistor (instead of 20 kohm)
- C91 use 18 pF capacitor (instead of 27 pF)
The Omega Main Board can be configured to support either V9958 VDP (recommended) or V9938 VDP. To support V9958 VDP the board should be configured as follows:
- Do not install the following components:
- Transistor: Q2
- Capacitor: C43
- Integrated Circuit: U43
- Note: C43 and U43 also used for PAL clock generation. They must be installed if PAL video standard support is desired
- Install a wire links JP3 and JP4 in 2-3 position for V9958 VDP
To support V9938 VDP the board should be configured as follows:
- Install the following components:
- Transistor: Q2
- Capacitor: C43
- Integrated Circuit: U43
- Install a wire links JP3 and JP4 in 1-2 position for V9938 VDP.
- If using NTSC video standard install a wire link instead of C93 to avoid floating inputs on U43
- Warning: Incorrect setting of JP3 will damage VDP
- 0x90 - 0x91 (aliases 0x92 - 0x93) - Printer Port
- 0x90: Write: Strobe (Bit 0)
- 0x90: Read: Busy (Bit 1)
- 0x91: Write: Data
- 0x98 - 0x9B - V9938 Video Display Processor (VDP)
- 0x98: Read/Write: VRAM Data
- 0x99: Write: Register Select / VRAM Address
- 0x99: Read: Status Register
- 0x9A: Palette access
- 0x9B: Indirect register access
- 0xA0 - 0xA2 - YM2149 Programmable Sound Generator (PSG)
- 0xA0: Write: Register Select
- 0xA1: Write: Register Value
- 0xA2: Read: Register Value
- 0xA8 - 0xAB - 8255 Programmable Parallel Interface (PPI)
- 0xA8: i8255: Port A - Primary slot select register
- 0xA9: i8255: Port B - Keyboard matrix row input register
- 0xAA: i8255: Port C - Keyboard matrix column output and cassette interface output register
- 0xAB: i8255: Command Register
- 0xB4 - 0xB5 (aliases 0xB6 - 0xB7) - RP5C01 Real Time Clock (RTC)
- 0xB4: RTC: Write: Register select
- 0xB5: RTC: Read/Write: RTC data
- 0xFC - 0xFF - Memory Page Select
- 0xFC: Read/Write: Page 0
- 0xFD: Read/Write: Page 1
- 0xFE: Read/Write: Page 2
- 0xFF: Read/Write: Page 3
- 0xFFFF (Memory I/O, slot 3) - Sub slot select register
- Slot 0
- 0x0000 - 0x7FFF (32 KiB): Main ROM, mapped to Flash ROM 0x00000 - 0x07FFF
- 0x8000 - 0xBFFF (16 KiB): Logo ROM, mapped to Flash ROM 0x08000 - 0x0BFFF
- 0xC000 - 0xFFFF (16 KiB): Unused
- Slot 1: Cartridge Slot 1
- Slot 2: Cartridge Slot 2
- Slot 3: Expanded slot
- Slot 3, Sub slot 0
- 0x0000 - 0x3FFF (16 KiB): Sub ROM, mapped to Flash ROM 0x10000 - 0x13FFF
- Slot 3, Sub slot 1
- 0x0000 - 0xFFFF (64 KiB): User ROM #1, mapped to Flash ROM 0x20000 - 0x2FFFF
- Slot 3, Sub slot 2
- 0x0000 - 0xFFFF (64 KiB): Main RAM (memory mapper)
- Slot 3, Sub slot 3
- 0x0000 - 0xFFFF (64 KiB): User ROM #2, mapped to Flash ROM 0x30000 - 0x3FFFF
Omega runs C-BIOS - an open source BIOS for MSX computers. It can also run the original MSX2* BIOS from computers with a similar slot organization and hardware specifications, for example Sanyo* PHC-23J and Philips* NMS 8250.
Omega uses three ATF16V8/GAL16V8 SPLDs (U12 - U14) for address decode and various other logic. The SPLD fuse maps (JED files) are provided in Mainboard/SPLD directory of this repository. The SPLDs are implemented using Flash/EEPROM technology and can be programmed by commonly available EPROM programmers, such as MiniPro TL866. The source code (PLD) files are also provided in the directory mentioned above. If needed, they can be modified, for example to change the slot mapping. Use GALasm to compile PLD files to JED fuse maps.
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Version 1.4
- Updates for a memory pager workaround:
- Use 2-pin jumpers instead of 3-pin
- Jumpers are connected by traces on the back side. To implement the workaround - cut the traces and install jumpers as needed
- Note: This version uses the original CUI/TE DIN 8 connector footprint
- Updates for a memory pager workaround:
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Version 1.3eu
- Modifications implemented by Jordi Solis:
- Workaround for memory pager issues - limit number of bits used by memory pager
- Cutout on the back of the board to allow using right angle slot connectors
- Use more common in the EU DIN 8 connector footprint
- Modifications implemented by Jordi Solis:
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Version 1.2
- Fix the known issues of version 1.1
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Version 1.1
- Fix the known issues of version 1.0
- Use DIN-8 connectors with standard MSX/MSX2 pinout for RGB and Cassette interfaces
- Move keyboard pull-ups to the motherboard
- Add LC filters for VDP and RGB encoder
- Add RESET / NMI header
- Connect slots pins 44 and 46 to GND
- Add polyfuse for joystick ports
- V9938/V9958 support: Add a switch (JP4) to select between CSYNC to TTL level shifter for V9938 or connect CSYNC directly for V9958
- Add Color Bus header
- Use ADM691A mircoprocessor supervisor
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Version 1.0
- Initial version
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Version 1.2
- Memory pager issues:
- Some software that writes and reads back memory pager to determine the installed memory size does not work correctly. This is because Omega memory pager implements all 8 bits regardless of the installed memory size, so all 8 bit are read back.
- Some software intentionally writes page numbers bigger than number of memory pages present in the system and expects the page number to "roll over". This doesn't happen on Omega becase it completely decodes all 8 bit of the page number
- When using right angle slot connector, cartridge interferes with the back side of the board
- Memory pager issues:
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Version 1.1
- Top silkscreen: R30 should be 1k (lower case 'k')
- Top silkscreen: L2 and L3 should be 5.6uH
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Version 1.0
- Top silkscreen: References R8 and R36 are swapped. The values are indicated correctly on the silkscreen.
- Top silkscreen: The values of C48 and C82 are swapped. C48 should be 0.1 uF, and C82 should be 1.5nF.
- Top silkscreen: Pal Clock Generator dotted line area should also include U43 and C43.
- Top silkscreen: "M" logo and the project URL are missing.
- Schematic: The pinout for 74AHCT32 IC (U37 - U39) is incorrect.
- Schematic: The /RD and /WR signals in subslot register select (U38C, U32D) are swapped.
- PCB: Keyboard connector (J11) interferes with printer port latch (U24). Use a straight pin header instead of a right angle one.
- Schematic: A pull-up is needed on V9938 VDP /INT output (pin 25), as it is an open drain output.
- PCB: MSX Cartrige Slots need to be rotated 180 degrees. Pin 1 of cartrige slot should be in top left position.
- Schematic: CXA1645 needs TTL level SYNCIN, while V9938 provides 2.4 V - 4.8 V signal at CSYNC. A level shifter is needed.
- Schematic: PSG clock divider 74HCT74 U35A /Q output (pin 6) should be connected to D input (pin 2), and CLK signal should be connected to CLK input (pin 3).
- Schematic: Audio low pass filter op amp plus input (pin 3) should be connected to VCC/2.
- Schematic: /VDP_WAIT has two pull-up connections to RR2 and to RR5. It should be connected only to RR2.
- Schematic: SW1 should be connected to the ground, SW2 should be left not connected.
- Schematic: Joystick "Left" and "Right" are reversed.
- Schematic: V9939 requires 5% tolerance power supply. Replace ADM693 with ADM691