ZiLOG Z-80 SIB User Manual page 20

Figures 3.4,1
and 3.4,2
symbolically represent
the
function
performed by
the CTC
in
each mode. The
flip-flop between
the
CTC and USART
is used
to
convert the pulse signal from the
CTC into
a
50%
duty cycle signal required by the USART.
Table 3.4.3 shows
the time
constants
to
be loaded into the
CTC in
order to generate the indicated baud
rate.
In
addition
to the
baud rate clocks provided by the CTC,
external RS232-level clocks may be used. This selection
is
made by applying jumpers
at J2, as shown
in
Table
3.4.2:
SIGNAL
JUMPER
J2
TxCO
14
RxCO
13
TxCl
6
RxCl
5
TxC2
16
RxC2
15
TxC3
1
RxC3
12
INO
9
INI 10
IN2
8
IN3
7
CTC CLKO
2
CTC CLKl
3
CTC CLK2
4
Where:
TxC
=
USART Transmitter Clock
RxC =
USART Receiver Clock
IN External RS232 Clock
CTC CLK
=
50% Duty Cycle CTC Clock
TABLE
3.4,2: USART Clock Inputs