A2Pico Reference Hardware

This repository is the home of the A2Pico reference hardware. Please refer to the upstream repository at https://github.com/oliverschmidt/a2pico for general information on A2Pico.

Hardware Revision History

Version 1.4 is the innitial design with 3x 74LVC245 and 1x 74HC08 to prove the concept. However it is obsolete as it does not switch off the Expansion ROM ($C800-$CFFF), which is always available and could cause data bus conlisions if used with other cards that use this memory space.

Version 1.5 switches off the Expansion ROM ($C800-$CFFF) when $CFFF is accessed or when reset is issued, and switches it back on again when the slot memory is accessed (IOSelect).

Version 1.6 combines 3 of the logic chips into a PLD. 74LS08, 74LS133 and 74LS02 are replaced by ATF22V10.

The RPI usage is as follows:

GPIO	Usage
0	UART TX
1	UART RX
2 - 13	A0 - A11
14	R/W
15 - 22	D0 - D7
26	ENBL
27	IRQ
28	RES

Version "n" has support for a MicroSD card with no ExtROM capability.

The RPI usage of the "n" versions is as follows:

GPIO	Usage
0	SPI RX
1	SPI CSn
2	SPI SCK
3	SPI TX
4	NMI
5 - 12	A0 - A7
13	DEVSEL
14	R/W
15 - 22	D0 - D7
26	ENBL
27	IRQ
28	RES

Version 1.7 is a direct successor of v1.4. Changes are replacing the 7408 by a 7411, data direction is controlled now by the Raspberry Pi Pico, which allows for all memory locations to be emulated, ENBL has an option to be is driven by a voltage divider for minimum latency, a USB "back power" option is included.

The RPI usage is as follows:

GPIO	Usage
0	UART TX
1	DATA dir
2 - 13	A0 - A11
14	R/W
15 - 22	D0 - D7
26	ENBL
27	IRQ
28	RES

Versions 2.4 and 2.5 are a new hardware variant of v1.7 - TH and SMD respectively. The major change is that A0-7 and D0-7 are multiplexed and an SD card interface is added. The RPI usage is as follows:

GPIO	Usage
0	UART Tx
1	UART Rx
2	ENBL
3 - 10	AD0 - AD7
11 - 14	A8 - A11
15	R/W
16	PHI1
17	RES
18	IRQ
19	CMD
20	DAT0
21	DAT3
22	CLK
26	AL-OE
27	D-OE
28	DDIR