User`s manual

DIGITAL-LOGIC AG MSMP5 / P3 SEN/SEV Manual V1.6A
65
I/O Ad-
dress
Read/Write
Status
Description
03F8h R / W Baud rate divisor (low byte) - This byte along with the high
byte (03F9h) store the data transmission rate divisor.
bits 7-0 = Data bits 0-7 when the Divisor Latch Access
Bit (DLAB) is 1
03F9h R / W Baud rate divisor (high byte) - This byte along with the low
byte (03F8h) store the data transmission rate divisor.
bits 7-0 = Bits 8-15 when DLAB = 1
03F9h R / W Interrupt enable register
bits 7-4 = Reserved
bit 3 = 1 Modem status interrupt enable
bit 2 = 1 Receiver line status interrupt enable
bit 1 = 1 Transmitter holding register empty inter-
rupt
enable
bit 0 = 1 Received data available interrupt enable
when DLAB = 0
03FAh R Interrupt identification register - serial port 1
bits 7-3 = Reserved
bits 2-1 = Identify interrupt with highest priority
00 Modem status interrupt (4th priority)
01 Transmitter holding register empty (3rd
priority)
10 Received data available (2nd priority)
11 Receiver line status interrupt (1st
priority)
bit 0 = 0 Interrupt pending (register contents can be
used as a pointer to interrupt ser-
vice routine)
1 No interrupt pending
03FBh R / W Line control register - serial port 1
bit 7 = Divisor Latch Access (DLAB)
0 Access receiver buffer, transmitter hold-
ing register, and interrupt enable register
1 Access divisor latch
bit 6 = 1 Set break enable. Forces serial output
to spacing state and remains
there
bit 5 = Stick parity
bit 4 = Even parity select
bit 3 = Parity enable
bit 2 = Number of stop bits
bit 1 = Word length
00 5-bit word length
01 6-bit word length
10 7-bit word length
11 8-bit word length
03FCh R / W Modem control register - serial port 1
bits 7-5 = Reserved
bit 4 = 1 Loopback mode for diagnostic testing of
serial port.
bit 3 = 1 User-defined output 2
bit 2 = 1 User-defined output 1
bit 1 = Force Request To Send active
bit 0 = Force Data Terminal Ready active
Continued...