Specifications

Serial Communications (16C452)

Reset Control (RESET*)

The ZT 8809A contains power-up and pushbutton reset circuitry that

drives the RESET* input signal at the serial ports. The reset forces

the serial ports into an idle mode in which all serial data activities are

suspended. The Modem Control register (MCR) and its associated

outputs are cleared. The Line Status register (LSR) is cleared except

for the THRE and TEMT bits, which are set. All functions of the

device remain in an idle state until programmed to resume serial data

activities. Table 8-1 illustrates the effect of reset on the serial ports.

Table 8-1

16C452 Reset State.

Interrupt Enable Register Reset All bits low (0-3 forced

and 4-7 permanent)

Interrupt Identification Reset Bit 0 is high, bits 1 & 2 low

Line Control Register Reset All bits low

Modem Control Register Reset All bits low

Line Status Register Reset All bits low, except bits

5 and 6 are high

Modem Status Register Reset Bits 0-3 low,

bits 4-7 input signal

SOUT Reset High

Intrpt (RCVR Errs) Read LSR, Reset Low

Intrpt (RCVR Data Ready) Read RBR, Reset Low

Intrpt (THRE) Read IIR,

Write THR, Reset Low

Intrpt (Modem Status

Changes) Read MSR, Reset Low

-Out2 Reset High

-RTS Reset High

-DTR Reset High

-Out1 Reset High

8-14