[Coco] CoCoNet status
robert.gault at worldnet.att.net
Tue Dec 30 09:03:15 EST 2008
Roger Taylor wrote:
> At 10:29 PM 12/6/2008, you wrote:
>> Have you tested this with a CoCo 1? Recent tests I've done have led
>> me to the conclusion that the CoCo 1 hardware is not capable of
>> transmitting 57600 bps through the bit banger port, although it can
>> receive data at that speed. My guess is that the opamp used for the
>> level translation to +/- 12 volts can't operate that fast. You will
>> probably have to lower the transmission speed or specify a CoCo 2 as
>> the minimum requirement.
> I confirmed that the PC is not receiving correctly at 57600 bps from
> both of my CoCo 1 systems. You can see junk bytes being received
> instead, but it looks like the same number of bytes, just not the data
> that was sent. 115200 bps obviously didn't work, either.
> Another thing I noticed. When you turn a CoCo on, it "transmits" a
> phantom character to the remote PC due to how BASIC sets up the PIA
> chips. At some point a start bit is seen by the PC which leads to a
> byte being framed. It could be that a break or partial break is
> transmitted. I haven't looked further into it.
The opamp used is the MC741C listed as having a slew rate of 0.5 V/us.
I'm not sure what this means in terms of baud but the 741 is not
adequate for high quality music.
The chip in the Coco3 is custom but seems to be a TTL inverter. If
typical TTL it should handle about 35 MHz.
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