UPGRADING REPAIRING PCs

170
Table 6.4 Overview of UART Chip Types Continued
Maximum Typical
UART Type Speed Buffer System Notes
16550A -> D Up to 16-byte 386/486 First chip suit
115000bps FIFO Pentium able for multi-
(115Kbps) tasking; can be
used as pincompatible
replacement for
socketed 16450
16650 Up to 230000bps 32-byte Specialized Faster throughput
(230Kbps) I/O cards, than 16650
ISDN terminal series adapters
16750 Up to 460000bps 64-byte Specialized Faster throughput
(460Kbps) I/O cards, than 16650,
ISDN terminal 16650 series
adapters
16950 Up to 921600bps 128-byte Specialized Faster throughput
(921.6Kbps) I/O cards, than 16550,
ISDN terminal 16650, 16750
adapters
Note
Chapter 6—Serial Ports and Modems
The previous specifications reflect maximum speeds available
with standard I/O card designs; some vendors use a clockmultiplication
feature that can double the effective speed of
some UARTs in some I/O card applications.
Identifying Your System UART
The minimum desirable UART chip is the 16550A series or above,
but older systems and inexpensive multi-I/O cards might use the
bufferless 8250 or 16450 series UARTs instead. Two major methods
can be used to determine which UARTs you have in a system.
MS-DOS Method (also for Windows NT)
Use a diagnostic program such as Microsoft MSD, CheckIt,
AMIDiag, or others to examine the serial ports. These programs also
list the IRQ and I/O port addresses in use for each serial port.
Because ports are virtualized under Windows, the reports from a
DOS-based utility will not be accurate unless you boot straight to a
DOS prompt and run the diagnostic from there.