This is a CMOS version (low power consumption) of the NS16450. IBM used this part in the IBM AT and updated the IBM BIOS to no longer rely on the bugs in the INS8250. Same as NS8250A with improvements so it can be used with faster CPU bus designs. This is a CMOS version (low power consumption) of the INS8250A and has similar functional characteristics. The INS8250A was used initially in PC clone computers by vendors who used "clean" BIOS designs.ĭue to the corrections in the chip, this part could not be used with a BIOS compatible with the INS8250 or INS8250B. INS8250AĪn improved version of the INS8250 using XMOS technology with various functional flaws corrected. It contains the same problems as the original INS8250. This is the slower speed of the INS8250 made from NMOS technology. The original IBM BIOS includes code to work around these flaws, but this made the BIOS dependent on the flaws being present, so subsequent parts like the 8250A, 16450 or 16550 could not be used in the original IBM PC or IBM PC/XT. This original UART has several race conditions and other flaws. The 8250 uses eight I/O ports and has a one-byte send and a one-byte receive buffer. Below is a table of the RS232-C signal assignments in the DB25 and DB9 connectors.
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