Technical data

3-14 Theory of Operation

RS-232 SIO Interface

The RS-232 interface has six modem control lines and an 8-bit DIO interface. It shares

the 25-pin D-sub connector with the SIO lines of the Utility Interface chip. For systems

that use HP-UX Compatible mode, you can use the Boot ROM’s Interface Conﬁgura-

tion Mode to conﬁgure the following parameters of the RS-232 interface:

• Select code from 0 to 31

• Interrupt level from 3 to 6

• Remote mode (for terminals) or local mode (for display monitors)

• Modem enable

For information about using the Interface Conﬁguration Mode, refer to Appendix A.

ISA Subset Bus Interface

The CPU board has a single ISA subset bus slot for an Apollo or 802.5 Token Ring

network interface board. The interface operates in programmed I/O mode only, which

precludes the following ISA bus features: DMA, Bus mastership, and some interrupts

(uses only three of eleven interrupts). The bus operates synchronously with the proces

sor, but at one fourth the frequency.

HP-IB Interface

The HP-IB controller is an RS-232 interface that has six modem control lines and an

8-Bit DIO interface that supports HP-IB devices.

DIO-II and SGC Controller Slot

This single slot has both a DIO-II connector and an SGC (Standard Graphics Connec

tion) connector to support either a DIO-II or SGC graphics controller. The graphics

controller board (or interface board for external controllers) connects directly to the

system’s DIO bus.

DIO Bus Interface

The DIO bus interface controls the address and data bus buffers, and performs the fol

lowing functions:

• Arbitrates the internal (CPU) bus and I/O (DIO) bus

• Controls processor board addresses, and the data and control bus buffer

• Provides interrupt timing

• Translates CPU control signals to DIO-II protocol and vice versa

• Generates cache addresses and cache control strobe timing