HP 400 Series Servicing Manual page 64

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:
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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:
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3-14 Theory of Operation
Select code from 0 to 31
Interrupt level from 3 to 6
Remote mode (for terminals) or local mode (for display monitors)
Modem enable
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