HP 13255 Technical Information page 21

13255
General Purpose Asynchronous Data Comm Module
13255-91089/19
Fev AUG-01-76
3.5
3.5.1
3.6
The transmit baud rate multiplexer (U25) is ptoqrammed with the spllt-
rate (SO,
51,
and
52)
switches and selects a frequency to ClOCK the
~AR~ at t~e desired baud rate. The transmit baud rates are selected as
follows:
52 51 50
TRANSMIT BAUD RATE
SC SC
~C
Custom Baud Rate
SO
SO
SC
4800
50 5C
SO 2400
~o
SC
~c
1200
5C
50
SO
300
5C 50 5C 150
~C ~C ~o
9600
~o
SO SO
Selected Receive Baud Rate
SC
=
Switch Closed
SO
=
Switch Open
TRANS~IT ~ANDSHAKE.
The
tr~nsmlt
handshake circuit orovldes
t~e
capability of handshaking
transmirted data with an PS232C control line. When the trans~it hand-
sha~e circuit Is enabled (THE Switch closed), the device receivinq the
transmission has the capability of siqnalinq a "busy" condition on the
CR
or
SA
control lines ann thus temporarily stoppinq data transmission.
Transmission is halted by turning off the Transmit Clock (TRC) to the
UART.
T~is
circuit is a 2-state, synchronous maChine that is clocked at
16
times the transmit haud rate. CB and 5B must be stable at the middle
of the last
sixte~nth
of the
la~t
stoo bit
of a
character with at least
l~O nanoseconns of setup time. The Off state of CB siqnals a "busy"
condItion. T~e On state of SR signals a "bUSY" condition unless ISS
(P2,
Pin
10)
is grounded, In which case the
Off
state of
SB
signals a
"husv"
cond~tion.
If a "bUSY" siqnal appears on
CB, SA,
or both, then
the transmission will
b~
held off.
PECFIVE HANOSHAKE.
The receive handshake circuit provides the capability of
~andshaktno
received data with an
RS232r
control line.