Parallel Input/Output Interface; Serial Interface; Introduction To Serial Circuitry; Setting The Baud Rate - Commodore Amiga Hardware Reference Manual

Parallel Input/Output Interface
The general-purpose parallel interface
is
a 25-pin male connector on the back panel of
the computer. This connector is generally used for a parallel printer.
For pin connections, see appendix E.
Serial Interface
A 25-pin D-type female connector on the back panel of the computer serves as the gen-
eral purpose serial interface. This connector can drive a wide range of different peri-
pherals, including an external modem or a serial printer.
For pin connections, see appendix E.
INTRODUCTION TO SERIAL CIRCUITRY
The circuit that controls the serial link to the outside world is called a UART, which is
short for Universal Asynchronous Receiver/Transmitter. The UART is able to commun-
icate at baud rates (bit-rate of transmission of data) that you preset. It can receive or
send data with a programmable length of eight or nine bits.
The UART is also capable of detecting overrun errors, which occur when some other sys-
tem sends in data faster than you remove it from the data-receive register. There are
also status bits that you can read to find out when the receive buffer is full or when the
transmit buffer is empty. An additional status bit is provided that indicates "all bits
sent." All of these topics are discussed below.
SETTING THE BAUD RATE
Baud rate (rate of transmission) is controlled by the contents of the register named
SERPER. Bits 14-0 of SERPER are the baud-rate divider bits. If you consider the con-
tents of these bits to be the number N, then N+1 color clocks (each 279.4 ns) occur
between samples of the state of the input pin (for receive) or between transmissions of
output bits (in the transmit mode).
240 Interface Hardware