using SPI as emulator for RS232 transmission

[zilog]

I have run out of UARTS, and need a serial TX channel for debug purposes. I need more performance of this channel than SW RS232 can provide (the application is interrupt-heavy), and therefore I am looking at using a SPI channel as for producing RS232 signals. If I could get the SPI data line to idle high between transmissions, then all would be fine since I could transmit the first bit being 0, and the rest as 7 bit data, and finish with a high idle level as stop bit.

My problem is that I cant find a way of configuring the SPI port to idle between transmissions, any ideas? I guess I could place an inverter at the SDO pin, and transmit all data inverted, but I would rather prefer to solve the problems in software than starting to cut traces up.

[Ttelmah]

You need a lot more.
Remember that SPI, is a synchronous system, so has no ability to guarantee timings at the sort of rates required by standard serial.Even if you only send 'seven bit' data, async, requires nine bits in the frame (start and stop bits), while SPI, only sends eight bits.
Look at the MAX3310. Has a SPI driven UART, RS232 buffer/level translator etc., all in one chip.

Best Wishes