maxim max3110 spi uart

[lewiseley]

hi
i have been using a software uart, but have now decided to dump it and go for the spi uart from maxim, i also use the i2c bus which i intend to drop as well, and go all spi.

i was hoping that you could detail what i will need.

i am looking to have multiple max 3110's and also frams ( 2 ) all hooked up on the spi bus, i was also considering providing an expansion port to allow another spi master to connect in as well.

are there any pitfalls i should watch out for, ( my chip is a 18f2680 ) , which is the most appropriate mode, do the lines need pullups etc.

any advice will be welcome.

thanks

[Ttelmah]

The MAX3110, works OK, but is a bit of a pig to get working. Basically, there are a couple of faults in the data sheet, and the 'example' C program supplied wth it, will only work to reliably receive data, if data transmission is taking place at the same time. I have posted in the past a set of interrupt driven drivers for this chip, and this is the way I'd go. So you would need the three SPI lines, a seperate 'select' line to each chip, and a seperate interrupt line from each chip. If you want another SPI master to be able to connect to your processor, then you will need to reserve the hardware SPI port for this, and use software SPI to drive the MAX chips (and any other slave devices). This brings a slight 'timing' downside, requiring the code to spend longer in the interrupt handlers, but should not be too bad...
No pull ups required. However if the SPI lines are going any significant distance, you may need to consider terminating networks.
How many serial ports do you need?. Remember you have two hardware UARTs already present on the 2680, and a Max 3110, has two sets of buffers supplied in each chip, so two of the Maxim chips, will give you four hardware ports with buffers (assuming no hardware handshaking is used).
Email me directly roger at ttelmah dot demon dot co dot uk, if you want to talk about using these chips.

Best Wishes

[Ttelmah]

Thinking on, the 2680, is one of the smaller chips, that only has the EUSART, not a EUSART+UART, so change the above comment to giving you three ports, not four.

Best Wishes