HP 13255 Technical Information page 20

13255
General Purpose Asynchronous Data Comm Module
13255-91089/18
Rev AUG-Ol-76
3.4.~
The select inputs of the receive baud rate multipleier (U35) are driven
bv the control reqlster.
The proper X16 clock rate is selected
t~
drive the
UART
receiver. The r~celve baud rates are selected as fol-
lows:
CONTROL
RfGTSTE'P
3
,
1
RFCF.IVE BAUD RATE
--------
----~------------~~-~------------~------
1
1
1
9600
1
1 0 4800
1
0 1
2400
1 0 0 1200
0
1
300
0 t 0
150
(If
134
Switch Open)
134.5 (If 134
Switch Closed)
0 0 1
110
0 0 0
F.xternal ClOCK
(If CBE
Switch Open)
Custom Baud Rate (If CAE Switch Closed)
The custom baud rate qenerator also consists of three 4-bit binary
~ounters
(U27, "17, and
U141.
These counters are proarammed with 12
switches to produce the desired baud rate. The counters qet preset
when the
~C
(Pin 15)
output of all three counters is true. The TC out-
put of the
la~t
counter is
aat~~
with the bus SYstem ClOCK to prevent
alltchinq and routed throuqh
A
O-tvpe tllo-flop to square the signal.