Rockwell Automation 1771-DB BASIC MODULE - Manual (Page 234)

Chapter
Call Routines 0–68 12
12 -44
Important: This call requires the BASIC module to be in 16 point mode
(page 1 -7).
Use CALL 49 to read up to 63 words of data from a remote DH-485 node
and place in the BTR buffer or a string within the BASIC module.
This call is useful for reading bar code data and sending it to the PLC
processor or an internal string. Once you set up and enable this operation,
it is performed transparently in the background while the BASIC module
executes a BASIC program in the foreground.
Refer to the DF1 Protocol and Command Set Reference Manual
(publication number 1770-6.5.16) for detailed information on DH-485.
If you choose an internal string, the first character increments to inform the
BASIC module that new data is in the string. The value of this character
wraps around from 255 to 0.
Execute CALL 49 once to set up the data transfer parameter.
PLC handshaking is used to initiate and notify completion of the transfer.
The BASIC module sends the DH-485 READ command you configure in
in this call to the remote DH-485 device you designate on the network.
1. The local PLC processor sets the output image table bit 14 to inform
the BASIC module to execute the DH-485 READ command you
configured in CALL 49.
PLC Processor
BASIC Module
PLC Backplane
Set Output Image Table
Bit 14
2. The BASIC module automatically issues the appropriate DH-485
READ command to the remote device on the DH-485 network.
The data and status are sent back to the BASIC module.
BASIC Module
PLC Processor
Remote Device
PLC Backplane
DH485
Data and Status
READ Command
Data
CALL 49: Read Remote
DH-485 SLC Data File
Tip