Mesa 4I23

• QUAD RS-232, RS-422 or 2+2
• RS-485 capable outputs
• Uses 16C550 FIFOed UARTS
• Access to all AT bus interrupts

The 4I23 is a low cost, four channel serial port card on a stackable PC/104 bus card. The 4I23 is available in three versions: quad RS-232, quad RS-422, and a model with two RS-232 and two RS-422 channels.
The 4I23 uses 16C550 type FIFO'ed UART's. These UART's have built-in 16 byte receive and transmit FIFO's. The 16 character FIFO's reduce interrupt overhead and allow higher data rates without losing characters. The receive FIFO's also increase the allowable interrupt latency. This is especially important when using programs like WINDOWS that disable interrupts for comparatively long periods of time.
Unlike many serial cards, the 4I23 is implemented with the 16 bit bus connector so that each of the four serial ports on the 4I23 can use any of the 11 available AT bus interrupts.