Texas Instruments 990 Maintenance Manual page 21

~-------
~
945408-9701
(DATA TRANSFER IS SERIAL)
0 2 3 4 5 6 7 8 9 10 11 12 13 14 15
MEMORY
ADDRESS
o
CHAR
(A) 130728A
0 0
x x x x x x x x
X :..- NOT USED
Figure 3-3. Input Character Transfer
MODULE
INPUT BITS
0
2
3
4,
6
7
•
• •
3.2.6 SAMPLE PROGRAM SEQUENCES. This paragraph contains sample program sequences to
illustrate the fundamental mechanics required for input and output operations. Actual routines are
more efficient by controlling these low-speed input/output operations with interrupts.
3.2.6.1 Echo Character. Figure 3-4 illustrates an instruction sequence that reads a character typed
on the keyboard of a 733 ASR/KSR Data Terminal, echoes .that character to the printer of that
device, and loops to read another character.
3.2.6.2 Output Character String. Figures 3-5 through 3-7 illustrate an instruction sequence that
outputs a character string to the printer of a Model 733 ASR Data Terminal. Figure 3-5 illustrates
the definition of the input and output CRU bits to the module. This is not necessary, but makes
subsequent reference to these bits easier. Figure 3-6 shows code that fetches a string of characters
for transfer to the data terminal.
This routine is called as follows:
BLWP @OUTASR
DATA BUFFER
where BUFFER is the name of the buffer containing the character string to be output. The final
character of this string must be the two's complement of the desired character.
Figure 3-7 illustrates a sequence that must be observed when transmitting a string of characters
to the printer 'of a Model 733 ASR Data Terminal. Since the baud rate of the module is set to four
times that of the data terminal printer, three null characters must be sent by the module to the
terminal with each character that is to be printed by the terminal.
14
Digital Systems Division