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+--- Thread: System 80 RAM Expansion (/thread-741.html)
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RE: System 80 RAM Expansion - Ernest - 01-12-2023
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
RE: System 80 RAM Expansion - RedskullDC - 01-12-2023
Hi Chesh, et al.
If you're in need of edge connectors, have a look at these right angle ones: https://www.aliexpress.com/item/1005005928852117.html
I recently purchased a few different types from them for some projects :
40pin for TRS-80
44pin for VTech Laser500
50pin for System 80 / Exidy Sorcerer
72 Pin for Laser3000/Cat
plus a couple of others.
All arrived safely.
Regards,
Leslie
RE: System 80 RAM Expansion - someone - 06-12-2023
(01-12-2023, 12:46 AM)Ernest Wrote: …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…
There shouldn’t be any issues having both SRAM and DRAM present if the address decoding logic is correct.
i.e. Ensure that the existing DRAM decoding doesn’t enable DRAM or associated data bus transceivers between 8000-FFFF.
As for using bus buffers and transceivers for the expansion module you’ll need to consider the ramfications of lengthening system bus signals. If they become too long or noisy bad things can happen.
(01-12-2023, 10:30 PM)RedskullDC Wrote: Hi Chesh, et al.
If you're in need of edge connectors, have a look at these right angle ones: https://www.aliexpress.com/item/1005005928852117.html
I recently purchased a few different types from them for some projects :
40pin for TRS-80
44pin for VTech Laser500
50pin for System 80 / Exidy Sorcerer
72 Pin for Laser3000/Cat
plus a couple of others.
All arrived safely.
Regards,
Leslie
An excellent find. Thanks!