A2retroNET RP2040

Directly connecting the Raspberry Pi RP2040 to the Apple II slot bus

Demo Program

This is a HW implementation of Oliver Schmidt's recommended designs.

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 However it is obsolete as it does not switch off the Expansion ROM ($C800-$CFFF), which is always available and could cause data bus conlisions if used with other cards that use this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

There is a suggested driver for a ProDOS block device for the "n" version.

However, there is a current need for development of a firmware for the "n" version for the RPI Pico to drive the IO with the A2 and the MicroSD card.