This is a redesign of the lo-tech.co.uk 2Mb ISA EMS board with some changes:
- All thru-hole instead of SMD, while retaining a rather compact format
- Simplified address decoding and storage circuits for less chip count
All design files and gerber files for PCB manufacturing are avaiable in the repository. The schematics schematics is also avaiable in PDF format.
The card was tested in modern replica of an XT computer like Xi8088 and Micro8088 without issues.
To configure the EMS, jumpers on J2 header are used.
Pins pairs 1 and 2 configure the Page Frame base address, while 3 and 4 configure the IO Port base address.
Page Frame Address:
| 1 | 2 | EMS Page Frame Base |
|---|---|---|
| X | X | C000h |
| - | X | D000h |
| X | - | E000h |
| - | - | Invalid |
Port Base Address
| 3 | 4 | EMS IO Port Base |
|---|---|---|
| X | X | 260-263h |
| - | X | 264-267h |
| X | - | 268-26Bh |
| - | - | 26C-26Fh |
(-=no jumper (opened), X=jumper (closed))
You need a memory manager to use this board. I'm including the LTEMM driver provided by lo-tech in this repository. Please refer to this page regarding the terms of use.
All ICs are in DIP package.
- C1,C4 ,C5 ,C6, C7, C8, C9, C10, C11, C12: 100nF, ceramic
- C2, C3: 10uF / 50v electrolytic caps
- J2 2x4 2.5mm breakable header
- RN1: resistor network, 10k, bussed, 5 pins
- RN2: resistor network, 10k, bussed, 9 pins.
- U1, U2, U3, U4: AS6C4008-55PCN (You don't need to fill all sockets: fit as much memory as you need starting from socket 1!)
- U5: 74LS139
- U6: 74LS245
- U7, U10: 74HCT688
- U8, U9: 74LS670
- ISA bracket: Keystone 9202, plus screws.
- Thanks to hkzab for publishing a similar design
- Thanks to lo-tech.co.uk for having published their schematics
- Thanks to Sergey for all his projects!