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5.2
Changing the Monitor Mode
The software monitor has several operational options.
Some options
should be selected before power turn-on and some after.
5.2.1
Baudot / ASCI I Code
The serial I/O processing routines can be operated in either
BAUDOT or ASCI I units.
The DSR terminal on the 8251 USART (pin 22
of the IC, terminal three of the I/O connector) is used to indicate
to the monitor which code is being used.
For ASCII code, terminal
three is connected to ground; for BAUDOT, to +5 volts.
The ASCI I
connection is normally furnished on the MCEM-8080.
This connection
must be made BEFORE power is appl ied to the MCEM-8080.
If the state
of the DSR connection is changed with power on and without first
performing a RESET, the result may be indeterminate
(fo~
example trans-
mitting a 5 bit character to an 8 bit USART, etc.).
The placement of
this jumper is shown in Figure B.l.
5.2.2
Half / Full Duplex (Echo / No echo)
In normal operation, characters that are input to the software
monitor in the form of commands or parameters are retransmitted out
to the output device so that the operator can view and verify them.
This is called echoing of the character.
If however, the MCEM-808o-
is to be used in a system which automatically echos the input character,
external to the MCEM-8080, this feature may be defeated (otherwise a
double echo would result, causing repeating of the input characters).
An example of a self-echoing I/O system is the serial
loop~connected
teleprinter in which the keyboard and printer are connected in series.
To defeat the echo feature, FF H should be written into location
0D
H.
This location is normally initial ized to
00
upon monitor entry and will
be re-initialized upon each new entry into the monitor.
The I (Insert)
command can be used to perform the change by typing:
• I D
t
000D 00,F F
000E 005-
The characters to be typed by the operator are underlined.
If the
double character transmission is occurring, it will appear as:
I I 0 D
t t
000D 00
L '
F F F F
000E 00
S
As above, underl ined characters indicate those typed.
Notice that only
one
S
appeared because the echo has been turned off by that time.
5-2
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