Firmware for the MEGA65 DM65PIC
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00-STM32F429_LIBRARIES
00-STM32F4xx_STANDARD_PERIPHERAL_DRIVERS
01-DM65PIC
bin
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README.md
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README.md

Firmware for the DM65PIC

MEGA65 Computer

DM65PIC_PCBs

MEGA65 is an open-source new and open C65-like computer. All hardware designs and all software are open-source (LGPL). Please visit www.mega65.org to learn more about it.

DM65PIC Peripheral Interface Controller

The DM65PIC is the peripheral interface controller for the MEGA65 computer. It is based on the STM32F4 microcontroller.

The purpose of the DM65PIC is to provide an interface to an original Commodore 65 prototype keyboard or a standard C64 keyboard and to provide joystick ports. Future versions will also be able to work with the MEGA65 custom keyboard and these keyboards will also be able to be used as standard USB HID devices e.g. while using emulators. Additionally we will implement the Commodore 65 user port in future versions.

Here is a foto of some prototype version of our custom PCB:

DM65PIC_PCBs

This GitHub repository is containing the firmware of the DM65PIC.

You can see a combination of a MEGA65 FPGA prototype (based on a Nexys 4 DDR board), a DMPIC65 prototype and a very first work-in-progress version of the firmware in conjuncton with a real Commodore 65 prototype keyboard in action on YouTube: https://youtu.be/5PpsEw80j3M.

Folder structure

00-STM32F4xx_STANDARD_PERIPHERAL_DRIVERS  STM32 CMSIS and standard peripheral drivers
00-STM32F429_LIBRARIES                    Tilen Majerle's STM32F4 library
01-DM65PIC                                Firmware for the DM65PIC
bin                                       Firmware binary and how-to-flash documentation
eagle                                     Hardware design for the PCB

The actual firmware is located within the file main.c in the folder 01-DM65PIC/01-DM65PIC/User.

How to flash

In the folder bin you always find the latest binary version of the firmware as a .hex file. There is also the file bin/README.md that explains you how to build a cable and how to flash the DM65PIC firmware using a Windows, OSX or Linux machine.

How to build

We used the free version of Keil uVision5. The free version is code-size constrained (32KB), but as our compiled firmware (including all the libs) is smaller than 32KB, the free version works fine.

After having installed the Keil IDE, just double click or open the file project.uvprojx in the 01-DM65PIC folder. As all paths are relative, you should be able to build without further modifications.

How the interface works

The DM65PIC is doing a matrix scan on the original Commodore 65 keyboard by letting current flow through the columns and then find out if a key is pressed by checking, if the current from the column arrives at a certain row. That means, we configure all "row pins" of the STM32 microcontroller as outputs (no pullup/pulldown resistor) and all "column pins" as inputs (pulldown resistor).

The following diagram is the basis for the matrix scan. It is taken from Commodore's original document c65manual.txt, chapter 2.1.2.


            +-----+-----+-----+-----+-----+-----+-----+-----+-----+            +-----+
            | C0  | C1  | C2  | C3  | C4  | C5  | C6  | C7  | C8  |            | GND |
            |PIN20|PIN19|PIN18|PIN17|PIN16|PIN15|PIN14|PIN13|PIN-4|            |PIN-1|
            +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+            +--+--+
               |     |     |     |     |     |     |     |     |                  |
               |     |     |     |     |     |     |     |     |                  |
               V     V     V     V     V     V     V     V     V                  |
+-----+     +-----+-----+-----+-----+-----+-----+-----+-----+-----+               |
| R0  |<----+ INS |  #  |  %  |  '  |  )  |  +  | œ   |  !  | NO  |               |
|PIN12|     | DEL |  3  |  5  |  7  |  9  |     |     |  1  | SCRL|               |
+-----+     +-----+-----+-----+-----+-----+-----+-----+-----+-----+               |
| R1  |<----+ RET |  W  |  R  |  Y  |  I  |  P  |  *  | <-- | TAB |               |
|PIN11|     |     |     |     |     |     |     |     |     |     |               |
+-----+     +-----+-----+-----+-----+-----+-----+-----+-----+-----+               |
| R2  |<----+ HORZ|  A  |  D  |  G  |  J  |  L  |  ]  | CTRL| ALT |               |
|PIN10|     | CRSR|     |     |     |     |     |  ;  |     |     +----------+    |
+-----+     +-----+-----+-----+-----+-----+-----+-----+-----+-----+          |    |
| R3  |<----+ F8  |  $  |  &  |  {  |  0  |  -  | CLR |  "  | HELP|          |    |
|PIN-9|     | F7  |  4  |  6  |  8  |     |     | HOM |  2  |     |          |    |
+-----+     +-----+-----+-----+-----+-----+-----+-----+-----+-----+          |    |
| R4  |<----+ F2  |  Z  |  C  |  B  |  M  |  >  |RIGHT|SPACE| F10 |          |    |
|PIN-8|     | F1  |     |     |     |     |  .  |SHIFT| BAR | F9  |          |    |
+-----+     +-----+-----+-----+-----+-----+-----+-----+-----+-----+          |    |
| R5  |<----+ F4  |  S  |  F  |  H  |  K  |  [  |  =  | C=  | F12 |          |    |
|PIN-7|     | F3  |     |     |     |     |  :  |     |     | F11 |          |    |
+-----+     +-----+-----+-----+-----+-----+-----+-----+-----+-----+          |    |
| R6  |<----+ F6  |  E  |  T  |  U  |  O  |  @  |  ã  |  Q  | F14 |          |    |
|PIN-6|     | F5  |     |     |     |     |     |  ^  |     | F13 |          |    |
+-----+     +-----+-----+-----+-----+-----+-----+-----+-----+-----+          |    |
| R7  |<----+ VERT|LEFT |  X  |  V  |  N  |  <  |  ?  | RUN | ESC +------+   |    |
|PIN-5|     | CRSR|SHIFT|     |     |     |  ,  |  /  | STOP|     +--+   |   |    |
+-----+     +--+--+--+--+-----+-----+-----+-----+--+--+-----+-----+  |   |   |    |
               |     |                             |                 |   |   |    |
               |     |                             |                 |   |   |    |
               |  +--+--+     /      (LOCKING)     |                 |   |   |    |
               |  |SHIFT+----+  +------------------------------------+   |   |    |
               |  | LOCK|                          |                     |   |    |
               |  +-----+                          |                     |   |    |
               |                             +-----+-----+               |   |    |
            +--+--+                          |           |               |   |    |
            |CRSR +------------+-------------+           +---------------+   |    |
            | UP  |        K1 PIN-21         |           |                   |    |
            +--+--+                          |   4066    |                   |    |
               |                             |  DECODER  |                   |    |
            +--+--+                          |           |                   |    |
            |CRSR +------------+-------------+           +-------------------+    |
            |LEFT |        K2 PIN-22         |           |                        |
            +-----+                          +-----------+                        |
                                                                                  |
+-----+           +-----+     /                                                   |
| NMI | <---------+RESTR+----+  +-------------------------------------------------+
|PIN-3|           |     |                                                         |
+-----+           +-----+                                                         |
                                                                                  |
                                                                                  |
+-----+           +-----+     /      (LOCKING)                                    |
| R8  | <---------+CAPS +----+  +-------------------------------------------------+
|PIN-2|           |LOCK |
+-----+           +-----+

Keyboard Notes:

1. The  64 keys under C0 through C7 occupy the same matrix position as
   in the C/64,  as does the RESTORE key.  Including SHIFT-LOCK, there
   are 66 such keys.

2. The  extended  keyboard consists of the 8 keys under the C8 output.
   Counting the CAPS-LOCK key, there are 9 new keys. The C/64 does not
   scan these keys.

3. The new CURSOR LEFT and CURSOR UP keys simulate a CURSOR plus RIGHT
   SHIFT key combination.

4. The  keyboard mechanism will be mechanically similar to that of the
   C128.

While scanning the matrix, the DM65PIC firmware stores the status of each single key in an array, that is then transmitted to the MEGA65 FPGA using the Nexys 4 DDR's General Purpose IO (GPIO) port "JB".

The protocol between the DM65PIC and the FPGA works like this: Cyclically, 128-bit are transmitted as 32 (4-bit) nibbles. Each nibble represents 4 bit within the above-mentioned matrix. Nibble #0 represents the keys INS/DEL, RET, HORZ/CRSR, F8/F7. Nibble #1 represents F2/F1, F4/F3, F6/F5, VERT/CRSR. And so on. Here is the full description of the data sequence:

nbls #0 - #17:   keyboard bits corresponding to the 9 columns of keys (see above)
nbl #18:         joystick 1: bit0=up, bit1=down, bit2=left, bit3=right
nbl #19:         bit0=joy1 fire, bit2=capslock key status, bit3=restore key status
nbl #20:         joystick 2: bit0=up, bit1=down, bit2=left, bit3=right
nbl #21:         bit0=joy2 fire, bit3=reset momentary-action switch status
nbl #22 onwards: expansion port connector

The nibbles are transmitted by setting below-mentioned "bit0" .. "bit3" pins of the "JB" port and then clocking pin "JB1". For synchronizing the transmission, the "start of sequence" pin "JB2" is used as soon as a new 128-bit package starts.

The FPGA is also able to communicate back to the DM65PIC, i.e. for transmitting the LED status; but this is not supported, yet in the current version of the firmware.

Here is the pin layout for the FPGA's "JB" port:

JB1  = PG8:  clock; data must be valid before rising edge
JB2  = PG9:  start of sequence, set to 1 on first nibble of a new 128bit sequence
JB3  = PG10: bit0 of output data nibble
JB4  = PG11: bit1 of output data nibble
JB7  = PG12: bit2 of output data nibble
JB8  = PG13: bit3 of output data nibble
JB9  = PG14: bit 0 of input bit pair
JB10 = PG15: bit 1 of input bit pair

Credits

  • Paul Gardner-Stephen: MEGA65 main developer
  • Deft: chief MEGA65 officer
  • doubleflash: DM65PIC hardware design
  • sy2002: DM65PIC firmware in this GitHub repository

Special thanks go to Tilen Majerle for supporting sy2002 in learning how to work with the STM32 toolchain and of course for creating the awesome STM32F4 library that we heavily used for creating the DM65PIC firmware.