ICS Advent COMM4AT/EX, Product Manual

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Manual Number: 00750-123-1 Page 11
Chapter 4: Technical Description
The COMM4AT/EX utilizes the 16C554 UART. This chip features programmable baud rate, data
format, interrupt control and a 16-byte input and output FIFO, and is functionally 4 16C550 UARTs.
The 16C654 UART is also available on this card, which has a 64-byte FIFO as opposed to the 16-
byte FIFO available in the 16C554.
Features
• ‘Shareable’ IRQs allow more than one port to share a single IRQ
• IRQs 3-7, 9-12, 15 supported
• 16C554 buffered Quad UART Standard
• 16 Bit address decode allows for easier integration
• Speeds up to 460.8 K bps
• Multiple clocking modes insuring compatibility with existing software products
Interrupt Status Port
The COMM4AT/EX provides the user with an I nterrupt S tatus P ort ( ISP ) for greater throughput
when servicing multiple ports on a single interrupt line. The ISP is a read only 8-bit register that
sets a corresponding bit when an interrupt is pending. Port 1 interrupt line corresponds with Bit D0
of the status port, Port 2 with D1 etc.
The ISP is located at Base+7 on each port (Example: Base = 280 Hex, Status Port = 287, 28F
etc.). This allows any one of eight locations to be read to obtain the value in the status register. All
four status ports on the COMM4AT/EX are identical, so any one of the four can be read to deter-
mine which interrupt is pending. In the following example Channel 2 has an interrupt pending.
Bit Position: 7 6 5 4 3 2 1 0
Value Read: 0 0 0 0 0 0 1 0