[Coco] Coco Digest, Vol 68, Issue 27

[Roger Taylor]

At 01:50 AM 1/18/2009, you wrote:
>Hi Roger and all, yes I can confirm that the 6551 does run clock/16 
>on the 0000 rate setting.  Had mine running that way for years with 
>a 14.4k modem for improved compressed throughput (modified clock /2 
>to get 57600).  The modem response codes and actual throughput did 
>confirm this rate.

Years ago I made the claim that I was using the 115200 bps setting in 
the RS-232 Pack and had it connected to many of my dial-up 
modems.  The modems have chips that mimick some of the older UARTs or 
even use those chips and would talk at 115200 bps.  My own unreleased 
ANSI/VT-100/VT-52 16-color graphical terminal program called NetMate 
was used for years to call into BBSes and transfer files.  Ultimaterm 
has to be set to (I think) the 450 baud or 50 baud (can't recall 
which one), which actually sets the 6551 to the 0000 bitrate 
(external clock / 16).  So, Ultimaterm can talk at 115200 bps 
through: CoCoPro! RS-232 Pak, Tandy Deluxe RS-232 Pack, and a custom 
hacked DC Modem Pak, or any cartridge using a 6551.

Some have used a twice as fast crystal to get 230.4k, and as you 
said, 57600 bps by using a /2 crystal.  Makes sense.  But what if no 
crystal is used?  I keep reading the 6551 has an internal baud rate 
generator.  This certainly doesn't mean an internal clock for all 
modes except 0000 ?  Certainly not.  :)




>>The 6551 ACIA should be able to run at 115200 bps by setting the baud
>>rate to 0000 which means (external crystal / 16).  Has anyone
>>confirmed this?

-- 
Roger Taylor

http://www.wordofthedayonline.com