Hi John,
I suggest that rather than trying to add the 32K and have to deal with timing issues between internal and external RAM, which will be a bit of a nightmare with Dynamic internal and Static external, just use the Phantom function which will turn off the internal RAM and totally set up a full 64K RAM space with external SRAM.
By using the phantom feature you can just unplug the expansion board and your internal RAM is back running as normal.
You should be able to the whole 64K SRAM space with 2x 28 Pin 62256's and a single 74xx00 as someone suggested.
As Suzy said the SRAM has the bus management all built in with the !CE & !OE pin control.
edit: Use one NAND gate as an inverter for the !MREQ, feed it's output to one input of a second NAND gate, the second input will be the A15 and the second gates output will be the !CS of your 32K SRAM from 8000h - FFFFh.
Ernest
I suggest that rather than trying to add the 32K and have to deal with timing issues between internal and external RAM, which will be a bit of a nightmare with Dynamic internal and Static external, just use the Phantom function which will turn off the internal RAM and totally set up a full 64K RAM space with external SRAM.
By using the phantom feature you can just unplug the expansion board and your internal RAM is back running as normal.
You should be able to the whole 64K SRAM space with 2x 28 Pin 62256's and a single 74xx00 as someone suggested.
As Suzy said the SRAM has the bus management all built in with the !CE & !OE pin control.
edit: Use one NAND gate as an inverter for the !MREQ, feed it's output to one input of a second NAND gate, the second input will be the A15 and the second gates output will be the !CS of your 32K SRAM from 8000h - FFFFh.
Ernest
