Read Only Storage (Ros) - IBM 6360 Product Support Manual

TIMER
DMA
INTERRUPT
CONTROLLER
ICROPROCESSOR
NO CLOCK
RAM
I
J
I
J
I
J
I
I
I
I
I
BUS BUFFER 1
I
ASYNC
PRINTER
LINK
KEYBOARD
ADAPTER
DISPLAY
ADAPTER
DISKETTE
ADAPTER
Figure 6-4. System Bus Isolation Dur-
ing BAT
Read On
Iy
Storage (ROS)
Read Only Storage is sev~ral electron-
ic chips on the system card. It is a
permanent storage area for the Basic
Assurance Test (BAT) , Resident
Non-Automatic Diagnostics (RNA), Ini-
tial Program Load (IPL), and Memory
Record program.
The instructions in ROS are a perma-
nent part of the system hardware and
cannot be changed. ROS is a s tor age
area which can be read from, but can-
not be written into.
Initial Program Load is a sequence of
instructions stored in ROS that are
automatically executed after each POR.
These IPL instructions make it possi-
ble to load a program into the system.
I nterrupt Controller
As tile microprocessor moves and con-
trols data, some system conditions may
need attention. When these conditions
occur, an interrupt request will be
made to the microprocessor by the
interrupt controller. The following
interrupt requests are listed in their
order priority and are maskable inter-
rupts.
Level
o -
Incoming data for printer
sharing/3277 DE
Level
1
- Transfer data to
commo data link
Level
2
- Printer and Mag Card
data transfer
Level 3 - Keyboard incoming data
Level
4
- Diskette interrupt
Level
5
- Not used
Level
6
- Software timer
Level 7 - Error on commo
data link
When the microprocessor completes the
instruction it is processing, it per-
mits the interrupt. Any low level
interrupt can be interrupted by a
higher priority interrupt request
(Figure 6-5). Once the maskable
interrupt routine is complete, the
main program will continue from where
it was interrupted.
Chapter 6. System Electronics/Power Supply 6-5