17: USER COMMUNICATION INSTRUCTIONS
17-32 « FC4A MICROSMART USER’S MANUAL »
Sample Program – User Communication TXD
This example demonstrates a program to send data to a printer using the user communication TXD2 (transmit) instruction,
with the optional RS232C communication adapter installed on the port 2 connector of the 24-I/O type CPU module.
System Setup
The name of BUSY terminal differs depending on printers, such as DTR. The function of this terminal is to send a signal
to remote equipment whether the printer is ready to print data or not. Since the operation of this signal may differ depend-
ing on printers, confirm the operation before connecting the cable.
Description of Operation
The data of counter C2 and data register D30 are printed every minute. A printout
example is shown on the right.
Programming Special Data Register
Special data register D8105 is used to monitor the BUSY signal and to control the
transmission of print data.
The MicroSmart monitors the DSR signal to prevent the receive buffer of the printer from overflowing. For the DSR sig-
nal, see page 17-30.
Special DR Value Description
D8105 3
While DSR is on (not busy), the CPU sends data.
While DSR is off (busy), the CPU stops data transmission.
If the off duration exceeds a limit (approx. 5 sec), a trans-
mission busy timeout error will occur, and the remaining
data is not sent. The transmit status data register stores
an error code. See pages 17-11 and 17-27.
printer may not work correctly and may be damaged.