ACT apricot - SIO Overview

SERIAL INTERFACE
the circuitry for interfacing between the system processors
and
the two serial communication channels. A description
of each
connection to the SIO is provided at the end of the
chapter.
The data selector allows the programmer to select the
clock source which determines the transmit and receive
baud rates for
the RS232C channel.
Due to the relative complexity of the SIO compared with
other programmable devices on the System Board, a brief
overview of
the device is presented in the following
paragraphs.
Subsequent paragraphs describe the internal
structure and the utilisation of the device within the system
in more detail.
SIO Overview
The SIO is a peripheral device, which performs the
function of an intelligent two-channel parallel to serial/
serial
to parallel converter. The two channels (designated
Channel A and Channel BJ are totally independent of each
other and can be programmed to operate in either
asynchronous or synchronous serial data communications
modes.
Once programmed with the required serial data
communications mode, the processors are able to view the
SIO as two simple parallel input/output ports for the
majority of data transfer operations; one bi-directional port
for each channel. The SIO provides all the necessary
facilities for organising
data transfers over the two serial
channels.
These include:
(aJ Conversion of the parallel data into the correct
serial
data format for transmission over the selected
serial
channel. In asynchronous modes, this involves
the automatic insertion of start, stop and parity bits,
and assembling the parallel data into the correct
number of serial bits per character.