Manual for GR 1687 Megahertz LC Digibridge.
Compliments of Stepan Novotill.

Genrad no longer supports the 1687 and parts are no longer available.

These 99 png sheets were scanned at 600dpi from the original Genrad
1687 manual, and special care was taken to preserve the halftones.

The SXC2316B aka MK28XXX ROMS in this digibridge have been known to
die of old age. This used to be a common pinout.

Here is the pinout of the MK28xxx series. CS depends on part number.
   A7    1           24   Vcc
   A6    2           23   A8
   A5    3           22   A9
   A4    4           21   CS3
   A3    5           20   CS1
   A2    6           19   A10
   A1    7           18   CS2
   A0    8           17   D7
   D0    9           16   D6
   D1   10           15   D5
   D2   11           14   D4
  GND   12           13   D3

The 2716 does not have the needed chip select logic.
    +--------------+
 A7 |1    +--+   24| VCC
 A6 |2           23| A8
 A5 |3           22| A9
 A4 |4           21| VPP
 A3 |5           20| /OE
 A2 |6           19| A10
 A1 |7    2716   18| /CE
 A0 |8           17| D7
 D0 |9           16| D6
 D1 |10          15| D5
 D2 |11          14| D4
GND |12          13| D3
    +--------------+

So it probably makes sense to stuff the data from the 2Kx8
Mask ROMS into an 8kx8 EPROM or EEPROM chip with an active
high chip select pin for use with A15 and upper two address
lines for A11 and A14 as follows:
   C28187M -> 1800-1FFF
   C28186M -> 1000-17FF
   No Data -> 0800-0FFF
   C28145M -> 0000-07FF
WRONG: To replace these ROMS with ordinary 2764 EPROM you will need to
WRONG: make a socket adapter with the following pin connection changes:
WRONG:    EPROM-Vpp-pin-1 connects to +5V
WRONG:    EPROM-PGM-pin-27 connects to +5V
WRONG:    EPROM-/CE-pin-20 connects to GND
WRONG:    EPROM-/OE-pin-22 connects to ROM-/CE-pin-20

These ROMS can be read on an EPROM programmer as a 2716
if you jumper out the chip-select ping in an adapter socket.

...Stepan