Rockwell Automation 1771-DB Basic Module User Manual - Series A - Manual (Page 28)

Using the Serial Ports
Chapter 4
4–4
Important: The program port always resets the most significant bit of all
its data inputs. The range of each byte of data is 0 to 127 (7F
H
). On output,
the module transmits all bits as specified when using the PRINT CHR()
command except for the XOFF (13H) character. The range of each byte of
data is 0 to 255 (OFF
H
).
Important: The program port automatically inserts a CR, LF sequence
after the 79th character column. Use CALL 99 to reset the column counter
to zero to allow PRINT page width’s in excess of 79 characters.
You enter BASIC programs through a dumb ASCII terminal, such as an
industrial terminal in alphanumeric mode. Refer to section 4.3.2,
“Connecting a T3/T4 Industrial Terminal to the Program Port”.
Use the XOFF/XON commands to disable outputs from the program port
in the following way.
1. Use XOFF only on PRINT statements.
2. When XOFF is received during a PRINT, data output and program
execution are suspended immediately.
3. When XOFF is received at any other time, program execution
continues until a PRINT is encountered. When a PRINT is
encountered program execution is suspended.
4. Use XON to resume program execution.
The program port accepts uppercase or lowercase input, however, the
input receiver changes all commands, keywords or variables to upper
case before storing in memory, thus:
u10 print “hello”(CR)
appears as
10 PRINT “hello”
when listed.
4.3
Program Port (continued)
4.3.1
Using the XOFF/XON
Commands for the
Program Port