ZiLOG Z-80 SIB User Manual page 57

RESET AND INITIALIZE ALL FOUR USARTS
USART
LD
CUSARTO
LD
B,4
ULOl LD A,0
OUT
(C)
,A
OUT
(C)
,A
OUT
(C)
,A
LD A,
RESCOM
OUT
(C)
,A
ft
/
O
1 dPIKjU
OUT
(C)
,A
T
r\
TV
C
T
n^^M
OUT
(C)
,A
DEC
C
IN A,
(C)
INC
C
INC
c
INC
c
DJNZ ULOl
RET
RESCOM EQU 40H
SIBMOD
EQU 8EH
SIBCOM
EQU
37H
;
LOWEST PORT - CONTROL
THREE INTERNAL RESETS-EXT RESET
SET UP TESTING MODE
AND ENABLE BOTH TR AND RCV
CLEAR OUT RECEIVER BUFFER
RESET USART TO ACCEPT
MODE BYTE
8
BIT ASYNCHRONOUS
TRANSMIT AND RECEIVE-
ERROR RESET
4.1,3
Baud Rate Generation
The SIB will not function unless the three baud rate
generators are
running (actually only
the baud rates
connected
to the
channels
in
use
must
be
functioning)
.
The
first three channels of CTC
are used to
generate baud
rates. There are three possible clock inputs
to the
baud
rate CTC:
1/2 phi
from the MCB, 1/2 phi from the SIB, and
1/32 phi from the SIB. Jumper connections
at J3
determine
which
of
these clocks are input
to
the CTC when
in
the
counter mode.
In
the timer mode, the system clock
is
used
as
a
time base.
Jumper connections
at J2
determine which CTC
outputs drive each
of the
USART transmit
and
receive clocks.
The CTCs may
be
programmed
to
operate
in
either the counter
mode
(47H)
or the timer mode
(07H) (see
ZBO-CTC Product
Spec). The following routine will generate one baud clock
in the
timer mode and two others
in
the counter mode:
49