
CD2481
—
Programmable Four-Channel Communications Controller
180
Datasheet
Bit 4
Reserved; returns
‘
0
’
when read.
Bits 3:2
Mvct [1:0]
Modem Vector bits are set by the CD2481 to provide the lower two bits of the vector
supplied to the host CPU during an interrupt acknowledge cycle. Modem vector is
decoded as follows: Mvct [1] = 0, and Mvct [0] = 1.
Bit 1:0
Mcn [1:0]
Modem channel number is set by the CD2481 to indicate the channel requiring
modem interrupt service.
9.5.4.3
Modem (/Timer) Interrupt Status Register (MISR)
When the host receives a modem interrupt, the following status is provided in this register:
Bit 7
DSR changed
A logic
‘
1
’
indicates that a change has been detected on the DSR* input. The change
detect is programmed in COR4 and COR5.
Bit 6
CD changed
A logic
‘
1
’
indicates that a change has been detected on the CD* input. The change
detect is programmed in COR4 and COR5.
Mact
Meoi
Sequence of
Events
0
0
0
Idle
1
0
0
Modem interrupt requested, but not
asserted
1
1
0
Modem interrupt asserted
0
1
0
Modem interrupt acknowledged
0
0
1
Modem interrupt service routine
completed
Register Name: MISR
Register Description: Modem Interrupt Status Register
Default Value: x
’
00
Access: Byte Read/Write
Intel Hex Address: x
’
88
Motorola Hex Address: x
’
8B
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
DSRChg
CDChg
CTSChg
Reserved
Timer2
Timer1
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Binary Value for Timer