IBM 770 manual Telephony Modem Function, Subsystems

I/O Address	IRQ	Level		DMA	Channel
0220–0233	(default)	IRQ	5 (default)DMA		0
0240–0253		IRQ	7	DMA	1 (default)
0260–0273		IRQ	10	DMA	6
0280–0293		IRQ	11	DMA	7
0388–038B	(synthesizer)

Telephony (Modem) Function

The telephony (modem) function provides the following settings:

Serial Port

COM1 (I/O: 03F8 - IRQ 4)

COM2 (I/O: 02F8 - IRQ 3) (default)

COM3 (I/O: 03E8 - IRQ 4)

COM4 (I/O: 02E8 - IRQ 3)

3-6 Subsystems