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.
Register/Signal
Reset Control
Reset
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
Register
bits 3-7 permanently 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
