User Manual

2.5 COM ports Comparison
The COM port of the 7521 series can be RS-232 or RS-485 as follows:
type Pins name
2-wire RS-485 Data+, Data-
3-wire RS-232 Txd,Rxd,Gnd
5-wire RS-232 Txd,Rxd,Gnd,Rts,Cts
The programming of the 16C550 is very different from the 80188’s
UART. The interrupt handling of the 80188 is also very different from the PC’s
8259.
7521/2/2A/3/4/7 Series Hardware User’s Manual, Ver. 1.5 Sep/2002, 7Mh-001-15 -----50