Rockwell Automation 1771-DB BASIC MODULE - Manual (Page 214)

Chapter
Call Routines 0–68 12
12 -24
1. When data is available from the port, the BASIC module
automatically transfers the data into the BTR buffer. The module also
checks the same port for data at the end of each line of BASIC code.
BASIC Module
PLC Processor
External Device
PLC Backplane
PRT2
PRT1 RS–232, RS–422,
or RS–485 Network AVAILABLE
DATA DATA
BTR Buffer
BYTE
COUNT
Reserved
2. The BASIC module places the byte count of the valid data into the
lower byte of BTR word 1 of the BTR buffer. The upper byte of
BTR word 1 is reserved.
DATA
BTR Buffer
BYTE
COUNT
BASIC Module
PLC Backplane
PLC Processor
Reserved
3. The BASIC module sets a bit in the PLC input image table to inform
the PLC processor that valid data is available. Bit 10 indicates that
data is available from PRT1 and bit 12 indicates that data is available
from PRT2.
PLC Processor
Set Input Image Table
Bit 10 or 12
BASIC Module
PLC Backplane PRT2
PRT1
DATA
BTR Buffer
BYTE
COUNT
Reserved