Z84C90

KIO Serial/Parallel Counter Timer

PS011802-0902

8

All control registers must be rewritten after a hardware reset.

RTSA, RTSB. Request to Send (outputs, Active Low). These signals are modem control

signals for their serial channels. They follow the inverse state programmed into their

respective serial channels, and are multiplexed with Port C, bits 4 and 3, respectively.

RxCA, RxCB. Receive Clock (inputs, Active Low). These clocks are used to assemble

the data in the receiver shift register for their serial channels. Data is sampled on the rising

edge of the clock.

RxDA, RxDB. Receive Data (inputs, Active High). These pins are the input data pins to

the receive shift register for their serial channels.

SYNCA, SYNCB. Synchronization (bidirectional, Active Low). In the Asynchronous

mode of operation, these pins act much like the CTS and DCD pins. Transitions affect the

Sync/Hunt status bit for their respective serial channels, but serve no other purpose. These

pins are multiplexed with Port C, bits 6 and 1, respectively.

TxCA, TxCB. Transmit Clock (inputs, Active Low). These clocks are used to transmit

data from the transmit shift register for their serial channels. Data is transmitted on the

falling edge of the clock.

TxDA, TxDB. Transmit Data (outputs, Active High). These pins are the output data pins

from the transmitter for their serial channels.

WT/RDYA, WT/RDYB. Wait/Ready (outputs, open-drain when programmed as Wait;

tristated when programmed as Ready). These pins may be programmed as Ready lines for

a DMA controller or Wait lines for interfacing to a CPU. As a Ready line, these pins indi-

cate (when Active Low) that the transmitter or the receiver requests a transfer between the

serial channel and the DMA. As a Wait line, these pins dictate (when Low) that the CPU

must wait until the transmitter or receiver can complete the requested transaction. These

pins are multiplexed with Port C, bit 7 and 0, respectively.

XTALI. Crystal/Clock Connection. (input).

XTALO. Crystal Connection. (output).

ZC/TO0–ZC/TO3. Zero count/Time-out (outputs, Active High). These four pins are out-

puts from the four counter/timer channels of the KIO. Each pin pulses High when its cor-

responding downcounter reaches 0.