View source for Universal Asynchronous Receiver/Transmitter

The '''Universal Asynchronous Receiver/Transmitter''' (usually initialized as '''UART''') was a functional unit which contained all the [[circuit]]ry needed to originate and interpret [[asynchronous serial line]] signals, including the serial-[[parallel]] conversion.

Initially, they were implemented with discrete components. In about 1970, Vince Bastiani of [[Digital Equipment Corporation|DEC]], together with engineers from Solid State Data Systems (in Long Island, New York) produced a complete UART in a single very early [[MSI]] [[integrated circuit|chip]]. This evolved into a standard part, produced in a 40-pin [[Dual Inline Package|DIP]] package by many manufacturers. The first, in 1971, was the Western Digital WD1402A; the Fairchild TR1402A, General Instruments AY-5-1013 and Intersil 6402 were others.

The parameters of the line ([[character]] size, [[parity]], number of stop bits, etc) are all selected by the inputs to the chip. The circuitry needed to produce the [[voltage]]s and [[current]]s needed by the particular interface type was outside the chip, so a UART could be used with either [[EIA RS-232 serial line interface|EIA]] or [[20mA current loop serial line interface|20mA]] interfaces.

The introduction of UARTs can be seen happening in early DEC [[PDP-11]] serial interfaces; the earliest, the [[KL11 asynchronous serial line interface|KL11]], used discrete components, not a UART chip, as did the [[DM11 asynchronous serial line interface|DM11]]; the [[DL11 asynchronous serial line interface|DL11]], and all others after that date, utilized UART chips, though.

Early UART chips only handled a single line; later on, '''DUART'''s appeared, with 2 lines per chip. The QUART (four lines) and OCTART (eight lines) followed. (In general, all the lines in these have to share a singled set of parameters.)

==Buffers==

With increased speeds, besides locking the DCE-DTE rate at 2x the communication rate, UART chips would need to increase their local [[buffer]] size to be able to send continuously. It has been reported that it did not help that a UART chip was released with a defective buffer, or that in some cases, the buffers would need to be enabled.

==Description==

The [[DZV11 asynchronous serial line interface|DZV11]] technical manual (below) includes a detailed description of the UART in Appendix A, 'IC Descriptions'.

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==External links==

*  [http://retrocmp.com/attachments/article/143/UART%20AY-5-1013.pdf General Instruments AY-5-1013A UAR/T: Universal Asynchronous Receiver/Transmitter]
* [http://www.bitsavers.org/pdf/dec/qbus/EK-DZV11-TM-001_DZV11_Asynchronous_Multiplexer_Technical_Manual_Jun78.pdf DZV11 asynchronous multiplexer technical  manual] (EK-DZV11-TM-001)

[[Category: Serial Lines]]
[[Category: Integrated Circuits‎]]