What do you mean by "input channel"? Do you mean serial input, or digital inputs or analog inputs?
Note that if you are using a PLC's comm port for programming and online monitoring, then that comm port buffer will be filled with host link commands sent by the TRiLOGI software and when you subsequently use the INPUT$(1) to read the serial port #1 you will get a lot of these host link command strings. If you are disconnecting the PC or Xserver from the PLC's comm port in order for it to connect to something else (e.g. barcode reader) you should execute a loop of INCOMM(1) until it returns -1. This ensure that the buffer is cleared before using it for interfacing to other devices.