IMS IMSAI 8080 User Manual page 357

for any purpose, whether it is to select or change the
selection of the interrupt interval desired, or whether it
is to change the current priority status register, or to
output a bit 7 to the special purpose circuitry supplied
by the user. Similarly, any time the output byte is
used to set or change the current priority status level,
bits 4, 5, and 6 must be also output according to the
desired interrupt interval selected.
written without changing does not cause any momentary
glitches or other effects.
PIC-8
User Guide
Revision 3
Any bit which is
i n - I S