说明：  8-bit Digital I/O Module with RS-485 Interface. This chip uses a slightly larger PIC (16C63A) so it has more RAM for a bigger packet buffer. This chip has a 128 byte buffer so long text strings can be sent to it for printing on a printer or any other device connected to it. Note that this chip also has a BUSY input (in addition to the STROBE line) so full handshaking with the printer is possible, improving the data throughput (Approx 8000 chars/sec).