A few days ago I came across Ben Eater's excellent video series on a breadboard 8-bit CPU. I thought I'd try to design my own with more memory and fewer chips. My design is here: https://github.com/DoctorWkt/eeprom_cpu

I've only built things in Logisim and VHDL before, not real 74LS chips, so if anybody can give me feedback that would be excellent.

I'm thinking of memory-mapping a UART into the design, so I can interface to it with a terminal program like Putty/minicom. So far I've only found this UART at Element14, the HD3-6402R-9Z. It seems to fit the bill but it costs AUD$29. Can someone recommend a different UART which might be a bit cheaper?

Anyway, thanks in advance for any tips, suggestions, ideas that you can provide.

Cheers, Warren

 

Hi,
Have you tried eBay for the 6402
http://www.ebay.com/itm/Harris-Intersil-CDP6402CE-CMOS-UART-I-O-IC-DIP40-x-1pc-/161390749633
E

 

I think you will find wiring and ringing in the physical machine to be less challenging if you stick to low speed CMOS rather than LSTTL, especially where edge triggered circuits are concerned.

Have you considered designing your own UART? That might be a very rewarding exercise.

 

Thanks Eric and Dick. I'll look at 74HC series and the 6402 UART.
Warren

 

hi Dr,
I used the 8251 Usart in my Z80 micro PCB's. memory mapped.
E
http://electronics.dit.ie/staff/tscarff/8251usart/8251.htm

If you wanted to upgrade your design, look at the Z84C90

 

UART/SCI comes in different names depending on the manufacturer.

Intel P8251 PCI
Intersil IM6402 UART
Motorola MC6850 ACIA
NXP SC28L91 UART
Rockwell R6551 ACIA
Synertek SY6551 ACIA
Western Digital W65C51 ACIA
Zilog Z8530, Z85C30 SCC

Check out W65C51 at Mouser

Also you might want to look at this 6502 forum that compares 65C51 with 28L91.

 

A few days ago I came across Ben Eater's excellent video series on a breadboard 8-bit CPU. I thought I'd try to design my own with more memory and fewer chips. My design is here: https://github.com/DoctorWkt/eeprom_cpu

I've only built things in Logisim and VHDL before, not real 74LS chips, so if anybody can give me feedback that would be excellent.

I'm thinking of memory-mapping a UART into the design, so I can interface to it with a terminal program like Putty/minicom. So far I've only found this UART at Element14, the HD3-6402R-9Z. It seems to fit the bill but it costs AUD$29. Can someone recommend a different UART which might be a bit cheaper?

Anyway, thanks in advance for any tips, suggestions, ideas that you can provide.

Cheers, Warren

Are you sure you want a UART? - They're pretty useful if you want to add an RS232 port, but adding memory is probably easier with a DMA chip - unless you're hooking it up with a serial interface.