Duart; Utility Serial Ports; General Purpose Timer/Counter; Parallel Input Port - Performance Computer PT-VME151A User Manual

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Section FUNCTIONAL DESCRIPTION

DUART

The Motorola Dual Asynchronous Receiver/Transmitter (MC68681 DUART) provides a General
Purpose Timer, Parallel Input and Output Ports, besides the dual Serial Port capability.

Utility Serial Ports

The DUART provides two general purpose asynchronous serial ports. Port "A" is equipped with
basic modem controls: DTR, DSR, RTS, CTS. Port "B" is transmit and receive data only. Both ports
are equipped with RS-232 line drivers and receivers. The baud rate for each port can be set indepen-
dently over the common asynchronous speed range (50 to 38.4K baud). The ports can be controlled
via interrupts or polled I/O.
If you recieved a Performance Computer Debugger (PTBUG) as part of your order, Port A of the
DUART will be set to 9600 baud, 1 stop bit, no parity. PTBUG ignores CTS and DTR and deasserts
RTS and DSR (false).
The Utility Serial Port interconnect is located on the front panel and uses a 14-pin dual row pin
header connector.

General Purpose Timer/Counter

The General Purpose Timer is a flexible user programmable 16-bit counter/timer. The clock source
of the timer is derived from the 3.6864 MHz crystal attached to the DUART. Parallel Output Port
pin 3 can be programmed as an output of the timer allowing EPAK boards to take advantage of this
timer function through the [+EPKIO] signal.
DUART parallel Input Port pin 2 is unconnected, therefore the "External (IP2)" clock sources iden-
tified in the Counter/Timer Mode and Source Select field of the DUART Auxiliary Control Register
(ACR[6:4]) are not valid choices.
This timer is used by OS-9 for its real-time clock. For detailed information on the DUART and the
General Purpose Timer/Counter refer to the MC68681 Multi-Function Peripheral Specification.

Parallel Input Port

Clear-to-Send

Data-Terminal-Ready

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Parallel Input 0 of the DUART is attached to the RS-232 Clear-to-Send (CTS) receiver for
Serial Port "A". To allow CTS to act as a hardware enable for the transmitter, CTS Enable
Transmitter bit (4) in DUART Channel A Mode Register must be set to 1. The state of this
control signal can be read from IP0 bit (0) of the DUART Input Port Register.
Parallel Input 1 of the DUART is attached to the RS-232 Data-Terminal-Ready (DTR) receiver
for Serial Port "A". The state of this control signal can be read from the IP1 bit (1) of the
DUART Input Port Register.
The DUART is capable of generating an interrupt to the 68040 if a change of state occurs on
this signal. To accomplish this, the Delta IP1 IRQ bit (1) of the DUART Auxiliary Control
Register must be set and the ACC registers associated with the DUART Interrupt Request must
be setup.