Hi

Can anyone help me with this schematic? It's for the Control Universal EuroBeeb card. The serial port has a 5v driver circuit (so I'm told) but I am not sure how to connect it. I will be linking it to a BBC Micro (RS-423, 6v level serial) but I am not sure how to read the schematic. It says there are two RXD and two TXD lines, and they are connected to a circuit I don't recognise, but look like op amps. There are + and - connections.

On the BBC end, I only have 0v and TXD / RXD / CTS / CTS. Would it be safe to plug the ov into the -ve side of the EuroBeeb's TX / RX lines, and BBC TXD/RXD tp the +ve side of the corresponding lines on the EuroBeeb?

I'm going off this http://mdfs.net/Info/Comp/BBC/CUBE/cube65.png - the serial connector is on the left hand side above the IC list (table).

Failing that, I suppose I should be connecting a proper RS-232 line driver (MAX232 - on order) to the ACIA, but I want to try and connect it to the BBC Micro first.

Thanks

JonB

RS-423 is an unbalanced to ground circuit. I think what you are looking for is an RS-422 hookup, which is balanced to ground. You need to use a pair of transceivers, such as the MAX13487, to make the connections.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

BDD is correct. The schematic calls out IC2 as a 26LS30 and IC4 as a 26LS32. These ICs are the standard RS-422 transmitters and receivers, respectively. In lieu of these devices or the device BDD references, you can use two 8-pin 75176 RS-485 transceivers, with one wired for receive only and the other for transmit only.

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Michael A.

I mentioned the Maxim parts because the 26LS30 is old silicon and limited in availability. Digi-Key, for example, doesn't stock it.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

Or I could bypass all of that and use a MAX232, I think. It's the same as the serial comms circuit on the Micro UK101, ACIA -> Line driver -> RS232. In order to do this I would take out those two transceivers and wire the ACIA TxD / RxD / 0v pins directly to the circuit on the MUK101 (removing its ACIA first, of course).


However... I've been talking with the guys over at stardot (the Acorn forum) and the consensus is the port on this card should be electrically compatible with the BBC micro's RS-423 interface. Apparently the EuroBeeb card can be configured like this with a couple of jumpers. Once talking to the BBC, you can use a sideways ROM to turn it into a coprocessor (over serial) which seems pretty kooky but sounds like fun.

I must say it is odd having this ENORMOUS 19" Eurocard rack with only two slots in use...

http://stardot.org.uk/forums/download/file.php?id=12024&mode=view

B&B Electronics has a lot of serial solutions, like external adapters to go from RS-232 to RS-422/485/etc.. You may not need to change your board at all.

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?