What UART should i use for my first computer?

[jmthompson]

cbmeeks wrote:

One option that might help the beginner is look for a PLCC44 to DIP44 converter on eBay. These are dirt cheap and will allow you to plug it in like a normal DIP...although they are longer in that they have 4 extra pins. Just be careful and read closely. I bought some once and didn't realize it was a PLCC44 to DIP40 converter (it dropped four pins).

I'm a bit late to this party, but I'd just like to add that I've had good luck with these Proto-Advantage adapters. They're a hair under $15 on Amazon and since they have no socket they don't cover the whole dang breadboard width. They're also a good way to practice your surface mount soldering as you'll need to attach not only the chip but also the surface mount pin headers along the bottom.

[TomC]

I'm also a bit late but wanted to note that Technological Arts (http://www.technologicalarts.ca/) offers some very nice PLCC adapters. The socket is vertically mounted so the whole thing takes the same space as a very long IC. They're working on a new site so you can't buy just now but I've bought a few of their adapters and found them well-made.

[Dr Jefyll]

TomC wrote:

They're working on a new site so you can't buy just now

Thanks for posting, TomC. I'm pretty sure I've seen these adapters on the Digikey site, so that's an alternative source.

The same goes for the Proto-Advantage adapters mentioned by jmthompson in the preceding post.

For this sort of product, two categories especially worth browsing are:

• Product Index -->Prototyping, Fabrication Products --> Adapter, Breakout Boards
  
  Product Index -->Connectors, Interconnects --> Sockets for ICs, Transistors - Adapters

-- Jeff

[Proxy]

just throwing my 2 sents into this.... for the simpliest possible Serial Interface to a modern machine, the UM245R is pretty good.
i used this thing in my very first breadboard computer, with a Z80 running at 10MHz. it can also reliably handle a 65C02 running at 16MHz without wait states.

it's a 5V/3.3V breadboard friendly breakout board for the FT245R, basically a complete UART and UART to USB Adpater in a single chip. (the board also has a USB-B Connector)
it's the most simplistic option available. all the CPU can do is read bytes from the receiving FIFO, or write bytes into the sending FIFO. there are also 2 output signals that can tell the system if there is space in the sending FIFO (TXE = 0) and if the receiving FIFO has data in it (RXF = 0).
but other than that, it has no extra features. no interrupts, timers, etc. it's purely for communication. (hooking it up through a 65C22 would make it more feature rich. allowing for interrupts when data comes in, etc)
and besides the decoding logic to actually access it, there is nothing extra required to get it running, just the 8 bit data bus and the 4 control signals (RD, WR, TXE, and RXF).
the baud rate, start/stop bits, etc can be changed on your PC when you connect it via USB.

sorry i just really love these single chip 8-bit to USB chips from FTDI. they are so damn convenient.

[pjeaton]

+1 for the (UM)FT245R. I'm using it on my 6809-based Vectrex and it works great, right up to 921,600 as a Forth terminal on my PC via USB.

Importantly, it has easy driver install and no hangups, unlike several other TTL to USB interfaces I've used.

You've sort of glossed over one of the key advantages it has; built in TX and RX buffers so, whilst you can use it via an interrupt, you don't need to because that's all handled on-chip, you can just poll it occasionally and empty the buffers accordingly.

My minimal decoding for the control lines is one dual 4-input NAND and one hex inverter, because that's what was it the box at the time, it could be done more efficiently with a '138 or '139.

[barrym95838]

pjeaton wrote:

+1 for the (UM)FT245R. I'm using it on my 6809-based Vectrex and it works great, right up to 921,600 as a Forth terminal on my PC via USB.

I confess that I'm not too good at interpreting data sheets. Can you use OSCO to drive an external FF to clock the rest of your device?

[Edit: I see that it's N/C on the UM245R DIP module, so never mind ...]

[cjs]

barrym95838 wrote:

I confess that I'm not too good at interpreting data sheets. Can you use OSCO to drive an external FF to clock the rest of your device?

[Edit: I see that it's N/C on the UM245R DIP module, so never mind ...]

It would be easy enough to connect up with a jumper wire, since it's not far from a couple of N/C pins on the module.

But if you're wanting to see if the internal oscillator there drives the output pin when an external one is not used (which isn't entirely clear from the data sheet, but why would they have the output if it did not?) you'd have to make sure it's programmed to use the internal one (and has >4 V power), which I suspect, from the presence of the crystal on that board, it's not.

[Individual_Solid]

Folks using the FT254RL (in UM form or just the chip) - how are you address decoding the control lines? Particularly the TxE and RxE. I'm currently struggling over a compact circuit over on page three/four of this thread.

[graeme.harker]

Individual_Solid wrote:

Folks using the FT254RL (in UM form or just the chip) - how are you address decoding the control lines? Particularly the TxE and RxE. I'm currently struggling over a compact circuit over on page three/four of this thread.

I put mine on a VIA

[Proxy]

Individual_Solid wrote:

Folks using the FT254RL (in UM form or just the chip) - how are you address decoding the control lines? Particularly the TxE and RxE. I'm currently struggling over a compact circuit over on page three/four of this thread.

I'm just using an SN74x541 with TXE on A0, and RXF on A1 with the rest connected to a pull-up resistor array. B0-7 are just connected to the CPU Data Bus.
the actual address decoding for it and the FT Chip is done by an ATF1502/1504 CPLD. it only takes 3 output pins for both (RD and ~WR for the FT, and ~OE for the 541).

[pjeaton]

Individual_Solid wrote:

Folks using the FT254RL (in UM form or just the chip) - how are you address decoding the control lines? Particularly the TxE and RxE. I'm currently struggling over a compact circuit over on page three/four of this thread.

I'm using a Dual 4-input NAND and a 4 Invertors for decoding RD and !WR, for RxE I'm using a 6522 VIA input, I'm not using TxE.

[boondaburrah]

I'm using a 74HC245 as a separate I/O device to put the status lines on the data bus whenever I select it and PHI2 goes high. Of course this will cause a collision if you ever try to write to the status lines, but the answer to that is: don't. Seems fine for a first build but I'll probably use a real UART later. The FT245R has been great for just getting my beginner compy off the ground though.

[BigEd]

Welcome to the forum!