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Document ID: DETR-3UFPFE |
PS/1 - What is a UART, and what type should I use?
Applicable to: United States
A Universal Asynchronous Receiver/Transmitter (UART) is a component of a serial port that acts as a buffer to hold incoming modem information until the Central Processing Unit (CPU) can accept it. The 16550 UART has a 16-bit buffer that acts as a temporary holding place for data until the processor requests the data. The 8250 UART, the standard a few years ago, uses a 1-bit buffer. In an environment such as OS/2 or Microsoft Windows, where more than one program can be running at one time, the 16-bit buffer found in 16550 UARTs may be more important since the CPU has the ability to multitask other applications than just the data in the serial port. Even in multitasking environments, an 8250 UART is acceptable at speeds below 9600 baud and should cause no data loss. Likewise, running at modem speeds above 9600 baud can be performed without problems with an 8250 UART in non-multitasking environments such as DOS.
Internal modems contain their own UART since they also act as serial ports. It is standard practice to include 8250 UARTs on 2400 baud internal modems, while most internal modems that operate at 9600 baud or faster include a 16550 UART. By contrast, external modems use the UART found in the serial port. All PS/1 computers contain 8250 UARTs, so if external modems operating at 9600 baud or faster in multitasking environments are desired, you may wish to attach a serial card that contains a 16550 UART.
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Hint Category |
Modems | |
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Date Created |
23-04-96 | |
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Last Updated |
14-12-98 | |
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Revision Date |
14-04-99 | |
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Brand |
IBM Aptiva | |
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Product Family |
PS/1 | |
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Machine Type |
2011, 2121, 2123, 2133, 2155, 2168 | |
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Model |
C01; C34; M01; NEA; T35; U35; A62; A82; A94; B82; C42; C92; G42; M82; S92; 081; 087; 131; 137; K37; N31; N81; 11E; 13T; 14C; 16E; 17A; 18A; 18T; 19C; 21C; 23C; 28A; 46M; 51D; D50; G11; G13; G43; G46; G49; G50; G53; M40; M46; P11; P13; P43; P50; P53; R04; R05; R06; R09; R38; R42; R43; R44; R84; R86; R87; RO3; S11; S13; S43; S45; S47; S48; S50; S53; W11; W13; W42; W43; W45; W50; W53; 20E; 22T; 24C; 24M; 28V; 39E; 41T; 43C; 45V; 48E; 50T; 52C; 55V; 72E; 74T; 76C; 78C; 79C; 81A; 82E; 84T; 86C; 87C; CC1; D53; G14; G44; G52; G54; G72; G76; G78; G82; NM1; P14; P44; P57; P71; P74; P76; P78; P84; R14; R15; R16; R17; R18; R51; R52; R57; R58; R62; R63; R67; R71; R89; R93; R96; R97; S14; S44; S54; S70; S75; S76; S78; S80; W14; W44; W48; W54; W67; W76; W77; W78; Z33; 31E; 33T; 37C; 38C; 51E; 54T; 56C; 57C; 88V; BB1; G57; G87; OR1; OR3; OR4; OR5; P89; R28; R29; R31; R74; R78; R82; R98; S55; S85; SR1; US1; W52; W82 | |
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