3 serial ports com1-com2, 4 floppy disk interface, 5 controllers – Compaq MSB900 User Manual
Page 27: 1 interrupt controllers, Serial ports com1-com2, Floppy disk interface, Controllers, Interrupt controllers, Digital-logic ag
DIGITAL-LOGIC AG
MSB900/L Detailed Technical Manual V1.0
27
5.4.3.
Serial Ports COM1-COM2
The serial channels are fully compatible with 16C550 UARTS. COM1 is the primary serial port, and is sup-
ported by the board's ROM-BIOS as the PC-DOS 'COM1' device. The secondary serial port is COM2; it is
supported as the 'COM2' device.
Standard: COM 1/2: National PC87317VUL: 2 x 16C550 compatible serial interfaces
Serial Port Connectors COM1, COM2
Pin
Signal Name
Function
in/out
DB25 Pin DB9 Pin
1
CD
Data Carrier Detect
in
8
1
2
DSR
Data Set Ready
in
6
6
3
RXD
Receive Data
in
3
2
4
RTS
Request To Send
out
4
7
5
TXD
Transmit Data
out
2
3
6
CTS
Clear to Send
in
5
8
7
DTR
Data Terminal Ready
out
20
4
8
RI
Ring Indicator
in
22
9
9
GND
Signal Ground
7
5
The serial port signals are compatible with the RS232C specifications.
5.4.4.
Floppy Disk Interface
This is not available with this product; use a USB Floppy.
5.5. Controllers
5.5.1.
Interrupt Controllers
An 8259A compatible interrupt controller, within the chipset, provides seven prioritized interrupt levels. Of
these, several are normally associated with the board's onboard device interfaces and controllers, and sev-
eral are available on the AT expansion bus.
Interrupt:
Sources:
Onboard used:
IRQ0
ROM-BIOS clock tick function, from timer 0
yes
IRQ1
Keyboard controller output buffer full
yes
IRQ2
Used for cascade 2. 8259
yes
IRQ3
COM2 serial port
yes
IRQ4
COM1 serial port
yes
IRQ5
LPT2 parallel printer (if present)
no *
IRQ6
Floppy controller
yes
IRQ7
LPT1 parallel printer
yes
IRQ8
Battery backed clock
yes
IRQ9
Free for user
no *
IRQ10
Free for user
no *
IRQ11
Free for user
no *
IRQ12
PS/2 mouse
yes
IRQ13
Math. coprocessor
yes
IRQ14
Hard disk IDE
yes
IRQ15
Free for user
no *
* It may depend on the LAN configuration.