Entering DB 1
The system program adopts DB 1 during a cold restart. The system
program checks to see if the inputs and outputs or IPC flags indicated
in DB 1 exist in their corresponding modules. If they are not present
there, a DB 1 error causes the CPU to go into the STOP mode and the
STOP LED flashes slowly. The CPU no longer processes your
program.
After you program DB 1 and the CPU accepts it during a cold restart,
the following rules apply:
•• Only the inputs and outputs indicated in DB 1 can access peripheral
modules via the process images (L.../T... ...IB, ...IW, ...ID, ...QB,
...QW, ...QD operations and logic operations with inputs and outputs).
Access to process image addresses not entered in DB 1 cause
addressing errors.
•• You can load peripheral bytes directly by bypassing the process
image using the L PB/L PY, L PW, L OY, L OW operations for all
acknowledging inputs, regardless of entries in DB 1.
•• You can transfer directly (T PB/T PY, T PW) to bytes 0 to 127 only
for the outputs indicated in DB 1. This is because the process image is
also written to during direct transfer. Writing to I/O addresses not
entered in DB 1 causes an addressing error.
•• Transfer without a process image :
Direct transfer to byte addresses >127 is possible regardless of the
entries in DB 1.
Direct transfer of byte addresses of the extended I/Os (T OY,
T OW) is also possible regardless of the entries in DB 1.
Multiprocessor Mode
CPU 948 Programming Guide
10 - 12 C79000-G8576-C848-04
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