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Data Memory circuit

A project log for YGRECmos

The YGREC architecture, this time implemented in CMOS

Yann Guidon / YGDESYann Guidon / YGDES 06/14/2017 at 22:260 Comments

The A1,D1,A2,D2,A3,D3 registers emulate a sort of multi-ported memory. However there is only one standard memory chip (or it looks like that with several chips to emulate a 16-bits datapath).

The circuitry is a bit unusual and requires some MUXes here and there because the result bus can go to the address bus or the data bus of the SRAM chip(s).

There are two cases to consider:

So basicly, the SRAM's address bus is selected between the RES bus or A1/A2/A3, that's a MUX4. 8 pieces of 74HC153/253 are required. The 253 adds a tristate output that will be handy for an eventual takeover of the bus for external inspection...

The SRAM's data bus is bidirectional and a MUX won't work. There are 3 registers connected to the data bus (D1/D2/D3) that can be written by the SRAM or the RES. The SRAM has tristate output and must be isolated from the RES bus. The solution is to separate them with a pair of 74HC573 or 74HC245. The /OE of one is the opposite of the other's /OE to prevent contention.

So to sum up: the Data RAM part of the system contains

That's already a nice board, with 48 bits going from the registers, 48 bits going TO the registers, 16 bits from the result bus and the untold number of control signals...

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