bluejay Posted February 20, 2021 Share Posted February 20, 2021 I'm trying to add some kind of serial interface to my 6502 computer, so it can transmit data to and from another computer or modem. I need a simple IC that can accept an 8 bit parallel input and turn it into a serial output, and vice versa. Is using a microcontroller the only option for this? Is there a way to create a circuit that can do this using logic gates? Thanks in advance. Quote Link to comment Share on other sites More sharing options...
emerson Posted February 20, 2021 Share Posted February 20, 2021 What about something like the 16450 or the 16550? I'm sure the people over at VCF could scare some up for you. Or try and hunt down some RS232 ISA cards... As for a DIY glue logic solution, that could get tough. You would need to recognize the 150% pulse width of the start bit to initiate your receiver and counter, then count 8 units of time (depending on your baud rate) and shift the data into a buffer on each count. The stop bit could clock the buffered data onto your parallel bus, or the data is shifted onto your bus and the stop bit clocks it into the receive register. Remember that RS232 has both positive and negative voltages so some type of level conversion as well as dual rail power supply is required. 1 Quote Link to comment Share on other sites More sharing options...
bluejay Posted February 20, 2021 Author Share Posted February 20, 2021 I looked through datasheets and other resources on the 16450 and 16550; I decided to use an 8250. It does all I need, it's simple, and it's cheap. I'll use a MAX232 with it to make it a proper rs232 compatible signal, because apparently that thing can create RS232 compatible voltages using a normal 5v line... Not sure how it works but apparently it does. Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted February 20, 2021 Share Posted February 20, 2021 If you end up using a micro, look into the MCP23008, two variants, I2C and SPI. Bi-directional, 16 bit variant is MCP23017. You can also jig something with a shift register and a MAX232 or 233 (no caps needed), like a 74HC595. 1 Quote Link to comment Share on other sites More sharing options...
emerson Posted February 20, 2021 Share Posted February 20, 2021 I knew there was an older version of the 16550 but couldn't think iof it. I'm glad you found it. I'm not totally sure how the MAX232 does it either but I can verify that they work. Some kind of charge pump oscillator? This may detract from a retro build but this FTDI module is nice. It offers full 9 pin serial support over USB. It supports RS232, RS422 and RS485. I started using it a few months ago and I like it so far. http://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT231X.pdf https://www.mouser.com/ProductDetail/FTDI/LC231X/?qs=Mv7BduZupUhUgQqAlkLw8A%3D%3D 1 Quote Link to comment Share on other sites More sharing options...
bluejay Posted February 20, 2021 Author Share Posted February 20, 2021 24 minutes ago, emerson said: This may detract from a retro build but this FTDI module is nice. It offers full 9 pin serial support over USB. It supports RS232, RS422 and RS485. I started using it a few months ago and I like it so far. http://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT231X.pdf https://www.mouser.com/ProductDetail/FTDI/LC231X/?qs=Mv7BduZupUhUgQqAlkLw8A%3D%3D It isn't really a "retro" build although I'm using all old school components, so if there is a new component that has a significant advantage I would definitely make use of it. However, that IC seems to only come in either a QFN or SSOP. DIP is needed as I will be using a lot of breadboarding. Thanks for letting me know of its existance though, Quote Link to comment Share on other sites More sharing options...
emerson Posted February 20, 2021 Share Posted February 20, 2021 44 minutes ago, bluejay said: It isn't really a "retro" build although I'm using all old school components, so if there is a new component that has a significant advantage I would definitely make use of it. However, that IC seems to only come in either a QFN or SSOP. DIP is needed as I will be using a lot of breadboarding. Thanks for letting me know of its existance though, The mouser link is the breadboard compatible module I use. The datasheet is for the chip itself. That was a bit confusing so I apologize. Quote Link to comment Share on other sites More sharing options...
bluejay Posted February 20, 2021 Author Share Posted February 20, 2021 30 minutes ago, emerson said: The mouser link is the breadboard compatible module I use. The datasheet is for the chip itself. That was a bit confusing so I apologize. Oh, okay. It's cool and all but I'd prefer a proper 9 or 25 pin RS232 serial port; and that FTDI module will require more dangling wires and loose components to accomplish essentially what a 8250 and MAX232/233 can do while everything is attached to the breadboard/PCB, and the more features it can provide isn't useful to me, as RS232 is all I need. Thanks anyways! Quote Link to comment Share on other sites More sharing options...
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