After making 3 simple pcbs, I'm ready to try something a little more complicated. I really need the breadboard serial port to be replaced with a pcb. The breadboard uses a 555 timer and a POT to generate baud rates. This worked, but if you bumped the table or the POT the baud rate would change. Not an ideal situation.
Motorola made a bit rate generator chip, the MC14411. Using a 1.8432 MHz crystal, this chip would generate all the common baud rates from 75 to 115200, and many others.
I created this pcb with a dip switch to select between the different baud rates.
I brought in the data bus to the bin headers, but instead of the address bus, I only have A15,A14,A13 and A0.
The MC6850 has three chip select pins, CS0, CS1 and CS2. I am going to let this pcb do its own decoding. This limits the location to one of 8 banks of 8k using this method, but that is fine since I don't have many devices to decode.
The A0 address line is used as a register select in the MC6850.
The board has two pin headers for the TX/RX lines. These would be hooked up to a serial to usb converter.
I never had this pcb manufactured. The first draw back to this design is the lack of a complete address bus. Meaning, this card would have to be the last card in the chain, as no other cards could be daisy chained off of it.
As you can probably visualize, after the rom module and the ram module are hooked up to the breadboard computer, nothing was really gained. There was still a lot of ribbon cables connecting the pcbs to each other and to the breadboards. Unless the pcbs where bolted down, they just kind of floated in the air from the ribbon cables picking them up.
It is time to take a step back.
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