This page helps hardware designers to design new hardware from scratch. If you simply want to build the official PCB, see build_pcb.md
- A STM32F103C8T6 or compatible board. You can find them for a few dollars online. The "blue pill" works out of the box and the older "black pill" requires minor modifications. The newer STMF4 "black pill" is not compatible.
- A USB-serial dongle for programming the STM32 chip, with a 3.3V USART.
- One or more SD card port(s) for your STM32. You can also solder wires on a SD to microSD adapter.
- One or more SD card(s).
- A male DB19 port (you can modify a DB25 port to fit) with a ribbon cable.
- One 10k-100k resistor if you need SD card hotplug capabilities or if you have multiple SD card slots.
- One 100nF decoupling capacitor for the SD card (optional but recommended).
- Do NOT connect USB data lines on the STM32. Use the +5V or +3.3V pin to power it if you are unsure. To power from USB, you need to modify the blue pill itself (see below).
You can use the PCB design provided in the PCB folder. See build_pcb.md for more information.
Note: If you build this project, please seriously think about putting multiple SD card slots. It quickly becomes a must have in many situations.
While this section is optional, you may want to do a few modifications to your blue pill board:
R10 is a 1.5k pull-up resistor required for USB operation of the STM32. Unfortunately R10 is connected to PA12 and this is connected to a very important data line on the ST ACSI connector.
This resistor may cause problems on some DMA chips, also this resistor tends to feed power from the data line back to the STM32 power pin if you turn on the Atari before the ACSI2STM unit, which is bad.
You may want to remove R10 entirely. For this you can either try to unsolder it (a quite difficult operation) or just destroy it with cutting pliers, then clean up residues. Check with an ohmmeter between the 2 pads of R10, you should see an open loop.
Removing R10 will compromise the ability to use USB on that blue pill board.
R9 and R11 are mounted in series between the STM32 and the USB port data lines.
Removing these resistors allow powering the STM32 with a USB cable.
Of course, removing R9 and R11 will compromise the ability to use USB on that blue pill board. USB is not used at all in ACSI2STM.
ACSI pin numbers, looking at the male connector pins:
---------------------------------
\ 01 02 03 04 05 06 07 08 09 10 /
\ 11 12 13 14 15 16 17 18 19 /
---------------------------
Use this table to match pins on the ACSI port and the STM32:
| ACSI | STM32 | PIN | Description |
|---|---|---|---|
| 01 | PB8 | D0 | Data 0 (LSB) |
| 02 | PB9 | D1 | Data 1 |
| 03 | PB10 | D2 | Data 2 |
| 04 | PB11 | D3 | Data 3 |
| 05 | PB12 | D4 | Data 4 |
| 06 | PB13 | D5 | Data 5 |
| 07 | PB14 | D6 | Data 6 |
| 08 | PB15 | D7 | Data 7 (MSB) |
| 09 | PB7 | CS | Chip Select |
| 10 | PA8 | IRQ | Interrupt |
| 11 | GND | GND | Ground |
| 12 | PA15 | RST | Reset (optional) |
| 13 | GND | GND | Ground |
| 14 | PA12 | ACK | Acknowledge |
| 15 | GND | GND | Ground |
| 16 | PB6 | A1 | Address bit |
| 17 | GND | GND | Ground |
| 18 | (nc) | R/W | Read/Write |
| 19 | PA11 | DRQ | Data request |
WARNING: Pinout changed since v1.0: PA8 and PA12 are swapped.
Notes:
- GND is soldered together on the ST side. You can use a single wire for ground.
- Reset is not strictly needed, but heavily recommended.
- Keep the wires short. I had strange behavior with cables longer than 10cm (4 inches).
- The read/write pin is not needed.
- You can build a DB19 out of a DB25 by cutting 6 pins on one side and part of the external shielding. Male DB25 are easy to find because they were used for parallel port cables or serial port sockets.
- You will have to power the STM32 separately (if you use USB, don't use a cable with data lines connected).
SD card pins
100nF 10k-100k
_||__ _/\ /\ /\__+3.3V
| || | | \/ \/
_________|_____|__|___
/| | | | | | | | |
/_|01|02|03|04|05|06|07|8|
| |__|__|__|__|__|__|__|_|
|09| |
|__| |
| ||
| Lock ||
Use this table to match pins on the SD card port and the STM32:
| SD | STM32 | PIN |
|---|---|---|
| 01 | PA4 * | CS |
| 02 | PA7 | MOSI |
| 03 | GND | VSS |
| 04 | +3.3V | VDD |
| 05 | PA5 | CLK |
| 06 | GND | VSS |
| 07 | PA6 | MISO |
| 08 | (nc) | RSV |
| 09 | (nc) | RSV |
If you want to use multiple SD cards, connect all SD card pins to the same STM32 pins except CS (SD pin 1).
Here is the table that indicates the STM32 pin for each CS pin of the different SD cards:
| ACSI ID | STM32 | Connect to |
|---|---|---|
| 0 | PA4 | SD 0 pin 1 |
| 1 | PA3 | SD 1 pin 1 |
| 2 | PA2 | SD 2 pin 1 |
| 3 | PA1 | SD 3 pin 1 |
| 4 | PA0 | SD 4 pin 1 |
Leave unused CS pins unconnected.
WARNING: Pinout changed in v2.0: PA0 was added, PBx were removed and unused SD card CS pins must not be grounded anymore.
Notes:
- If you need to hot swap your SD card, or if you want multiple SD slots, you need to put a 10k-100k pull-up resistor between +3.3V and PA6. A single resistor is enough if you have multiple SD card slots.
- The ACSI2STM module will respond to all ACSI IDs, whether a SD card is
inserted or not. Change ACSI_SD_CARDS and ACSI_FIRST_ID in
acsi2stm.hto change ACSI IDs, or see the table below to disable IDs by connecting pins to +3.3V. - The SD card had 2 GND pins. Connecting only one is enough.
- You should put decoupling capacitors of about 100nF between VDD and VSS, as close as possible from the SD card pins. If you use a pre-built SD slot module it should be properly decoupled already.
- Some microSD slot boards for Arduino have logic level adapters to allow using SD cards on 5V Arduino boards. This will reduce speed and compatibility. Connect SD card pins directly to the STM32 pins for best results.
- microSD to SD adapters are a quick, cheap way to obtain a microSD reader. Simply solder on the SD adapter pads. They aren't very reliable though.
Some pins can be used to configure each SD card slot:
| ACSI ID | STM32 | Connect to enable | Connect to disable |
|---|---|---|---|
| 0 | PB0 | SD0 write lock / GND | +3.3V |
| 1 | PB1 | SD1 write lock / GND | +3.3V |
| 2 | PB3 | SD2 write lock / GND | +3.3V |
| 3 | PB4 | SD3 write lock / GND | +3.3V |
| 4 | PB5 | SD4 write lock / GND | +3.3V |
When the pin is connected to GND, the SD card will be writable. When the pin is
left floating, the SD card will be read-only. You can connect this pin to the
physical write lock switch if you have a full size SD card reader with this
ability. This logic can be inverted or disabled using the ACSI_SD_WRITE_LOCK
define in acsi2stm.h.
When the pin is connected to +3.3V, the SD card is completely disabled (the ACSI ID is freed for other devices).
To use the RTC feature, you need to connect a lithium battery to the VB pin of the STM32. Using a CR2032 with a standard battery holder is recommended.
If you have these cheap "STM32 minimum development boards" from eBay, Amazon, Banggood or other chinese sellers, chances are that you have either a "blue pill" or a "black pill" board. "blue" or "black" refers to the color of the PCB.
WARNING: There are newer STM32F4xx boards also called "black pill". These newer boards are currently not tested. This section refers to older STM32F103C8T6 black pill boards.
The problem with black pill designs is that the onboard LED is wired on PB12 instead of PC13, messing with data signals.
You will have to desolder the onboard LED (or its current-limiting resistor right under).
If you want an activity LED, put an external one with a 1k resistor in series on PC13.
Other boards such as red pills were not tested and may require further adjustments.
If you have a unit built for 1.x or 2.x firmware, you need to make changes.
If you don't want to or can't make these changes, you can use the legacy firmware variant. See flashing.
You need to connect the ACSI pin 12 (RST) to PA15. It is optional, but stability will be greatly improved by doing that.
Solder PB0, PB1, PB3, PB4 and/or PB5 to GND to make SD cards permanently read-write. See the table mentioning these pins above for more details.
Solder PB0, PB1, PB3, PB4 and/or PB5 to +3.3V to disable the corresponding slots. See the table mentioning these pins above for more details.
- Do all changes required for 2.xx units
- Swap PA8 and PA12