Specifications

Theory of Operation
Table 3-2
Serial Communications Standards.
Parameter RS-232-C RS-423-A RS-422-A RS-485
Operation Single-ended Single-ended Differential Differential
Number Of
Drivers/Receivers 1/1 1/10 1/10 32/32
Maximum Cable
Length (Ft.) 50 4000 4000 4000
Maximum Data Rate †
(Bits per second) 20K 100K 10M 10M
† The ZT 8809A maximum data rate is limited to 56 Kbaud by the UART
A terminated twisted pair should be used to protect the integrity of the
RS-485 signals. A typical twisted pair has a characteristic impedance
in the range of 100 to 130 Ω, adequate for data transfer rates of up to
10 MHz. The RS-485 balanced inputs can be terminated by installing
resistors at locations R17 and R19, which are adjacent to connector
J6. The resistors should be 0.25 watt or greater and have a resistance
value equal to the characteristic impedance of the twisted pair.
3-7