[Coco] CoCoNet status

[Robert Gault]

Roger Taylor wrote:
> At 10:29 PM 12/6/2008, you wrote:
> 
>> Roger,
>>
>> 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.
>>
>> Darren
> 
> 
> 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.