aallen
Posts: 1
Joined: Sat Oct 21, 2017 3:33 am

Potential use case thoughts

Sat Oct 21, 2017 5:46 am

I am replacing an old VME computer that communicates with a 9U line card chassis that will not be replaced. The vme computer runs a program that simply sends/receives 2048 bytes to the hardware (chassis) that is not being replaced. Each byte is asynchronously sent using hand shake lines.

My question is does this seem like an appropriate use of a RaspberryPi 3? Creating a program that will handshake 2048 bytes (on the GPIO pins) 10 times a second. I am not a hardware guy and just want to get some opinions of people who use these single board computers.

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rpdom
Posts: 17737
Joined: Sun May 06, 2012 5:17 am
Location: Chelmsford, Essex, UK

Re: Potential use case thoughts

Sat Oct 21, 2017 7:20 am

That should be possible. I'm assuming you'd be sending the bytes via a 8-bit bus. 2048 bytes ten times a second gives a data rate of just over 20KHz which is easily within the spec of the GPIOs.

You'll need a buffer/level shifter to adapt the voltage levels of the hardware to the 3.3V levels of the GPIOs, but that is easy to do. Setting up an 8 bit parallel bus isn't too hard, but the GPIOs are usually used as individual lines, so you'll have to set each bit separately. That isn't difficult either. It's certainly all doable in Python using one of the GPIO libraries available.

Using a Pi might be overkill even. An arduino could probably do the job.

steveb4pi
Posts: 62
Joined: Sun Aug 11, 2013 6:12 pm

Re: Potential use case thoughts

Sat Oct 21, 2017 8:33 am

A Pi 3 is oiverkill == the Pi Zero will do this job just fine

Depending on the protocol, you may be able to use the Pi 'serial command terminal' RS232 (but see WARNING below) which is 'exposed' on the i.o pins (holes, in the case of the Zero) == the drawback is that not all the flow control (Request to Send, Clear to Send) lines are available (I believe flow control is implemented in software just fine)

NB for testing, I would recommend a serial to USB adaptor (so you can see whats coming out of the serial TxD on a PC)

WARNING The Pi serial link pins are 3v3 NOT +/-12v !!!

An alternative is to use the Pi USB with a suitable 'dongle' (eg micro-USB to RS232 or RS485 etc) == againa check the voltages (many 'dongles' use +/-6v rather than the 'proper' +/-12v which ancient kit may well demand)

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