Specifications

Serial Communications (82050)
Interrupt and Polled Communication
Serial data can be transferred and received either by polling status bits
or with interrupts. In a polled mode, the application program monitors
the Line Status register Data Ready and Transmitter Holding Register
Empty bits to determine when to transfer a character to the ACC or
when a character is available.
The ACC is capable of generating interrupts for applications that
cannot afford time wasted in polling for a status change. If enabled in
the Interrupt Enable register, a Transmitter Holding Register Empty
interrupt is generated when the transmitter is free to receive a
character. Also, if enabled in the Interrupt Enable register, a Received
Data Available interrupt is generated when a character is received by
the ACC.
RS-485 Serial
Communications
The ZT 8832 includes jumper selectable drivers and receivers for both
RS-232-C and RS-485 serial communication protocols. The two main
advantages of RS-485 over RS-232-C are an increased number of
drivers and receivers (32 of each, versus one of each for RS-232-C)
and increased transmission distance (4000 feet, as compared to 50 feet
for RS-232-C).
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 up to 10
MHz. The RS-485 balanced inputs can be terminated by installing
resistors at locations R13 and R14. The surface mount resistors must
have a 1206 case size, a power rating of at least 0.125 W, and a
resistance value equal to the characteristic impedance of the twisted
pair.
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