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• Technical Manuals
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Introduction

According to Mike Douglas' website there is a Rev. B and a Rev. C Altair FDC+. I myself have two Rev. B boards.

I am currently (Feb. 2024) using the FDC+ with the SSM IO4 and the IMSAI MPU-A on my working IMSAI with the WMC FPB-1 front panel.

EPROMS

According to the manual you should use an 8K (64KBit) 27C64 CMOS EPROMs. I have also tried with success a ST M2764A-2FI and an Atmel AT28C64B EEPROM.

S2 - PROM

see manual 2.3, p.5

ON  = 1 or closed = rocker down towards top PCB
OFF = 0 or open   = rocker down towards bottom PCB

A13 to A15 are always to 1 (ON)
7, 8 = not used

8 7 6 5 4 3 2 1
---------------
      A A A A A
    E 1 1 1
    N 2 1 0 9 8
---------------
- - 1(1 1 1 1 1)=> 1 1 1 (1 1 1 1 1) 0 0 0 0 0 0 0 0
                   ---------+++++++++--------+++++++
                   F        F        0       0
                   
- - 1(0 0 0 0 0)=> 1 1 1 (0 0 0 0 0) 0 0 0 0 0 0 0 0
                   ---------+++++++++--------+++++++
                   E        0        0       0
                   
If you set the PROM to E000h, then you can use the
complete 8K of the M27C64 EPROM.

The 1st ROM is at F800 (Altair Monitor, ALTMON)
    

• MITS - Altair 8800
• IMS Associates - IMSAI 8080
• North Star Computers Inc.
• S-100 Bus

• Mike Douglas: https://deramp.com/fdc_plus.html

• Enhanced Floppy Disk Controller for the Altair 8800 Computer, User's Manual, 8/2/16, v1.4
• Enhanced Floppy Disk Controller for the Altair 8800 Computer, User's Manual, 3/3/23, v1.9

1. (↑) Mike Douglas, https://deramp.com/fdc_plus.html