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DIGITAL-LOGIC AG MSB900/L Detailed Technical Manual V1.0
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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.