Filter
Top Products
Appendix
COM-2(PC)F56
B. Notes on Developing Driver Software
Internal Registers
COM-2(PC)F uses the NS16550 (National Semiconductor) as the
Asynchronous Communication Element (ACE). Within the
address range of each channel, the offset addresses 0 through 7
furnish access to the internal registers of each of the two ACE's.
Table 6.6. shows how functions relate to the internal registers. To
access the baud rate generator (defined on the next page), the
DLAB signal must be set high. For more details on NS16550,
refer to the National Semiconductor Data Book.
Table 6.6. Function Selection through Internal Registers
I/O Port Address DLAB *1 ACE Register (NS16550) Note *2
"Base Address" +0H 0 Receiver (Buffer register) R
"Base Address" +0H 0 Transmitter (Holding register) W
"Base Address" +1H 0 Interrupt Enable Register
"Base Address" +2H x Interrupt ID R
"Base Address" +2H x FIFO Control W
"Base Address" +3H x Line Control
"Base Address" +4H x Modem Control
"Base Address" +5H x Line Status
"Base Address" +6H x Modem Status
"Base Address" +7H x Scratchpad Register
"Base Address" +0H 1 Baud Rate Divider Register LSB
"Base Address" +1H 1 Baud Rate Divider Register MSB
*1 DLAB: Divisor Latch Access Bit in the Modem Status Register.
*2 R=Read only; W=Write only.