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Other functions provided by the 8253 are:
Relative Time Clock
Programmable Rate Generator
Event Counter
Binary Rate Multiplier
Digital One-Shot
Uni versal Asynchronous Recd ver/rransmitter CUART)
The 444 has two serial I/O ports.
Each port consists of a CART and one-third
of the programmable interval timer (PIT).
The UART is a programmable device
used for interfacing an asynchronous serial communication line to the paralld data
lines of the microprocessor.
It is made up of two separate and independent
sections: the receiver and the transmitter.
The receiver accepts the serial data, decodes the control bits and converts the
data bits to paralld data.
The decode function converts the serial Start, Data,
Parity, and Stop bits to parallel information and verifies the proper code
transmission by checking parity and the receipt of a valid stop bit.
The transmitter section converts the parallel data into a serial word which
contains the data, along with the start, parity, and stop bits.
Both the receiver and transmitter double-buffer data transfers with the processor.
The UART may be programmed as follows:
1.
The word length may be either 5, 6, 7, or 8 bits.
(The IMS
standard is 8 bits.)
2.
Parity generation and checking may be inhibited, and the parity may
be odd or even.
(No parity standard for IMS systems.)
3.
The number of stop bits may be one or two
(l
1/2 when transmitting
a 5-bi t code).
OMS uses 1 stop bi t.)
4.
The baud rate may be set from 75 to 19.2 K baud.
(9600 baud is
standard.)
IMS International
5000 Series Microcomputers/7.01.83jPage
35
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