Can I use this memory mapping on Zilog 80?

Thread Starter

Matyas Michalicka

Joined Mar 11, 2019
8
Hello! I am quite new to hardware memory mapping on microprocessors.

Z80 has 16 address lines, ROM has 13 and RAM has also 13.
I would use the A13 + MREQ with de-multiplexer to select each memory chip.
output.png
My question is: Can I use 8k ROM and 8k RAM in this configuration with Zilog 80?
 

Thread Starter

Matyas Michalicka

Joined Mar 11, 2019
8
Your ROM and RAM are each 8K.
Hence organize your CHIP SELECT into eight 8K blocks. Use three address bits, A15-A13, using one 74LS138.
what is the purpose of that?
and also, how can I use the I/O? It looks like Z80 is accessing ROM/RAM. F.e., I want a code in ROM to blink an LED on one data pin. how could I do that?
 

ronsimpson

Joined Oct 7, 2019
3,210
In blue, A13 directly to /CE ROM and A13 to CE RAM, and /CE to ground. ROM and RAM will fill all memory addresses.
In red, remove inverter, and CE to +5V. Addresses=(ROM, RAM, nothing, nothing) repeat throughout memory space.
1673500318043.png
 

Thread Starter

Matyas Michalicka

Joined Mar 11, 2019
8
In blue, A13 directly to /CE ROM and A13 to CE RAM, and /CE to ground. ROM and RAM will fill all memory addresses.
In red, remove inverter, and CE to +5V. Addresses=(ROM, RAM, nothing, nothing) repeat throughout memory space.
View attachment 285051
well, I want the CPU to access memory when it actually wants, not everytime as you have shown in this scheme. thats why I do utilize the MREQ' output.I tinkered with the circuit some more:
1673518309634.png
 

ericgibbs

Joined Jan 29, 2010
19,104
My question is: Can I use 8k ROM and 8k RAM in this configuration with Zilog 80?
Hi Mayas,
Your original circuit is already accessing 8k ROM and 8K ROM, Addr A0 thru A12, and the LS139.

What changes to the circuit are you asking for.?
E
 

ronsimpson

Joined Oct 7, 2019
3,210
In about 1980 I had a "boot loader" program that load a program into ROM from the serial port. There was some peek and poke commands that made trouble shooting easy.
 
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