Motorola MVME1X7P - Manual (Page 229)

Programming Model
http://www.motorola.com/computer/literature 3-31
3
Modem PIACK Register
The Modem PIACK Register is used to execute modem pseudo interrupt
acknowledge cycles to the CD2401.
When the Local Bus master initiates a read cycle to this register, the
PCCchip2 executes an interrupt acknowledge cycle to the CD2401 with
A7-A0 = $01. (Note that the PILR1 register in the CD2401 should be set
to the same value ($01) for the interrupt acknowledge cycle to operate
properly.)
To finish the local read cycle, the PCCchip2 drives the vector received
from the CD2401 onto the local data bus, and asserts TA*. Reads to this
register are termed pseudo interrupt acknowledge cycles because they are
normal read cycles on the Local Bus side but they are interrupt
acknowledge cycles on the CD2401 side of the PCCchip2. They are
necessary to support polled mode operation with the CD2401.
Note If this register is read when an interrupt is not present, the
interrupt acknowledge cycle times out with a TEA if the Local
Bus timer is enabled.
MIV7-MIV0 Modem interrupt vector bits 7-0 reflect the modem
interrupt vector driven by the CD2401 to the PCCchip2
during a pseudo interrupt acknowledge cycle.
ADR/SIZ $FFF42023 (8 bits)
BIT 7 6 5 4 3 2 1 0
NAME MIV7 MIV6 MIV5 MIV4 MIV3 MIV2 MIV1 MIV0
OPER R R R R R R R R
RESET X X X X X X X X