Lop Bus - HP 9020 Service Manual

Theory of Operation
2-29
lOP Bus
The 50-conductor lOP ribbon cable interconnects the motherboard with the lOP finstrate in slot
#2. The lOP finstrate handles internal peripherals as well as the
110
backplane. With eight select
codes per lOP and a full complement of internal peripherals, four select codes (select codes 2-5) are
available to the user at the four
110
backplane slots. The slots are physically numbered to corres-
pond to the select codes. Select codes have been programmed to the following defaults:
Select
Code
Usage
0 Display Alphanumeric
1 Display Graphics
2 110 Slot #2
3 110 Slot #3
4 110 Slot #4
5 110 Slot #5
6 Keyboard, Printer, Real-Time Clock,
Beeper, Optional Input Device
7 Internal Mass Storage
Select code 6 services the keyboard, printer, real-time clock, beeper, and optional input device via
a single interface. The beeper is a write-only device with programmable frequency. Data can be
sent to the printer via DMA by enabling select code 6 for DMA. Select code 6 is enabled for
keyboard and printer interrupts at all times. The real-time clock is set and read via program-
controlled transfers.
One or two additional lOP finstrates can be added. Each is connected by a 50-conductor ribbon
cable to a connector mounted on the processor stack door. The ribbon cable provides the lOP bus
from the finstrate to the connector. A 97098A
110
Expander can then be connected to the stack.
The
110
expander provides eight
110
slots with required signal buffering and power supplies. The
select code configuration at the
110
backplane is unaffected by additional lOPs. Select Codes 8-15
are assigned to the first additional lOP; select codes 16-23 are assigned to the second additional
lOP.