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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