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The MPD8251 Universal Synchronous/Asynchronous Receiver/Transmitter is designed
specifically for 8080 microcomputer systems but works w ith most 8-bit processors.
Operation of the 8251, like other I/O devices in the 8080 fam ily, is programmed by
system software for maximum flexibility.
In the receive mode, a communication interface device must convert incoming serial
form at data into parallel data and make certain format checks on the data. And in the
transmit mode, the device must format data into serial data. The device must also supply
or remove characters or bits that are unique to the communication form at in use. By
performing conversion and formatting services automatically, the USART appears to the
processor as a simple or "transparent" input or output of byte-oriented parallel data.
C /D
RD
WR
0
0
1
0
1
0
1
0
1
1
1
0
X
X
X
X
1
1
Operating Temperature
Storage Temperature . .
All O utput Voltages . .
A ll Input Voltages. . . .
Supply Voltages..........
COMMENT: Stress above those listed under "Absolute Maximum Ratings" may cause permanent
damage to the device. This is a stress rating only and functional operation of the device at these or
any other conditions above those indicated in the operational sections of this specification is not
implied. Exposure to absolute maximum rating conditions for extended periods may äffect device
reliability.
* T a = 25° C
North Star HSIO-4
cs
0
8251 -*• Data Bus
0
Data Bus -*• 8251
0
Status -*■ Data Bus
0
Data Bus-*- Control
1
Data Bus-*- 3-State
0
77
FUNCTIONAL
DESCRIPTION
BLOCK DIAGRAM
BASIC OPERATION
ABSOLUTE MAXIMUM
- 0°C to +70°C
RATINGS*
-65°C to +125°C
-0 .5 to +7 Volts
-0 .5 to +7 Volts
-0 .5 to +7 Volts
User/Technical Manual
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