izne/AC63092A minimalistic industrial computer running 6809/6309
AC6309 Main is an open-source printed circuit board by izne, from the izne/AC6309 repository on GitHub. It is a 2-layer board of 99.1 × 99.1 mm with 23 parts on 64 nets, routed with 615 tracks and 46 vias.
It is built around the 74HC00D and 74HC138. Its parts include 9 capacitors, 6 ICs, 2 connectors, 1 switch and 1 crystal. It belongs with the computers and single-board computers and retro computing and games boards of this library.
A minimalistic industrial computer core, based on Motorola 6809 architecture.
Proof of concept custom 8-bit industrial computer with minimal device count implementation. Modular, low-power design, allowing easy expansion and customization per use case.
AC29 is dedicated to my beloved father.
Current state of PCB design:
| Address range | Device | Size |
|---|---|---|
| $0000-$7FFF | RAM | 32KB |
| $8000-$8FFF | Extension port #1 | 4KB |
| $9000-$9FFF | Extension port #2 | 4KB |
| $A000-$AFFF | UART | 4KB |
| $B000-$BFFF | Extension port #3 | 4KB |
| $C000-$FFFF | ROM | 16KB |
The 32KB of RAM is allocated from the bottom of the address range $0000 to $7FFF. The ROM is allocated at top 8KB of the address space starting $C000 to $DFFF.
The I/O mapping is allowing compatibility with existing BIOS images having ACIA on address 0xA000.
Using the combination ROM image in Intel HEX format it needs first be turned into a binary image to be written to the EEPROM.
objcopy -I ihex -O binary combined.hex combined.bin
Write the resulting .bin file using the specially created EEPROM programmer for AT28C-series EEPROMs. Or any other.
promdude.exe -f combined.bin
As a note, burning the combined.bin (16K) onto 32K 28C256 has to be at the correct half. Optionally, a copy of combined.bin twice into the chip will do as well.
As the firmware is 16K and 28C256 (32K) chips are nowadays more accesible, two firmware images could be stored in the full 32K capacity of the chip. A ROM switching key to be implemented on the board, to switch the higher or lower part of the chip to be "visible" (A14) at boot.
The system communicates with a terminal via USB serial connection using the included ACIA device and its UART capability, coupled with an FTDI232 header. Terminal serial port settings: 115200 baud, 8n1, no hardware handshake yet.
The schematics and PCB design is made with KiCad
| Qty | Value | Footprint | References |
|---|---|---|---|
| 6 | 100 nF | Capacitor_THT:C_Disc_D3.0mm_W2.0mm_P2.50mm | C4, C5, C6, C7, C8, C9 |
| 4 | R_Network08 | Resistor_THT:R_Array_SIP9 | RN1, RN2, RN3, RN4 |
| 2 | 15pF | Capacitor_THT:C_Disc_D3.0mm_W1.6mm_P2.50mm | C2, C3 |
| 1 | 100 uF | Capacitor_THT:CP_Radial_D8.0mm_P2.50mm | C1 |
| 1 | 28C256 | Package_DIP:DIP-28_W15.24mm_Socket | U3 |
| 1 | 7.3728 MHz | Crystal:Crystal_HC49-4H_Vertical | Y1 |
| 1 | 74HC00 | Package_DIP:DIP-14_W7.62mm_Socket | U5 |
| 1 | 74HC138 | Package_DIP:DIP-16_W7.62mm_Socket | U6 |
| 1 | FTDI | Connector_PinSocket_2.54mm:PinSocket_1x06_P2.54mm_Vertical | J2 |
| 1 | HD63B09P | Package_DIP:DIP-40_W15.24mm_Socket | U1 |
| 1 | HD63B50 | Package_DIP:DIP-24_W15.24mm_Socket | U4 |
| 1 | I/O | Connector_PinHeader_2.54mm:PinHeader_2x20_P2.54mm_Vertical | J1 |
| 1 | Reset | Button_Switch_THT:SW_Tactile_Straight_KSL0Axx1LFTR | SW1 |
| 1 | W24257 | Package_DIP:DIP-28_W7.62mm_Socket | U2 |
It measures 99.1 × 99.1 mm and has 2 copper layers, 1.6 mm thick.
23 parts, built around the 74HC00D and 74HC138. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
From the izne/AC6309 repository on GitHub, at the commit this page was made from: the board is AC6309_Main/AC6309_Main.kicad_pcb and its schematic AC6309_Main/AC6309_Main.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Its repository states no licence, so its author keeps all rights: ask izne before reusing the design.
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