Title: 6551: 115k2
 Posted: Sat 01-Mar-97 at 12:33:07
Replies: 0

> Would you mind sharing on how to
make the thing to boost ya to 115.2
k????

Look at the 6551 control register,
which is at $D123 (if I remember
correctly)
when using a Black Box. The control
register determines the number of
Stop
Bits (bit 7), the sio word lenght
(bits 5+6), the receiver clock
source
(bit 4) and the selected baud rate
(bits 0-3). If you want 8N1 at 19k2,
you
Poke a %00011111=$1F in it. The baud
rate table is as follows:

3 2 1 0 Baud
------- ----
0 0 0 0 (XTLI divided by 16)
0 0 0 1 50
0 0 1 0 75
0 0 1 1 109,2
0 1 0 0 134,58
0 1 0 1 150
0 1 1 0 300
0 1 1 1 600
1 0 0 0 1200
1 0 0 1 1800
1 0 1 0 2400
1 0 1 1 3600
1 1 0 0 4800
1 1 0 1 7200
1 1 1 0 9600
1 1 1 1 19200

Provided you have a 1.8432 MHz
crystal (stock BB) you should get
115k2 by
POKEing $10 into $D123. I could not
test this because my modem doesn't
go
beyond 57k6.

My test was like follows:

Take a 1.8432 x 2 = 3.6864 MHZ CMOS
oscillator and divide the signal by
three and by two (to get 50% duty
cycle). Connect the divided signal
to
Pin 6 of the 6551 (disconnect the BB
capacitor). Pin 7 must float. Poke
$10 in the control register and you
get 57K6. I tested this with 38K4
too.
My modem told me the baud rates with
the connect message. If you loose
characters, than take into
consideration, that your E: device
might be
to slow.