
CD2481
—
Programmable Four-Channel Communications Controller
168
Datasheet
Bit 1
Framing error
–
indicates that a bad Stop bit has been detected.
Bit 0
Break
–
indicates that a break has been detected.
Note:
During an interrupt service routine, the host can use this register to provide a timer value as
detailed in the Receive End of Interrupt register. The host can only load one of the two timers in the
interrupt service routine.
RISRl
–
X.21 Mode
For X.21 operation, the CTS* pin is used as the
‘
I
’
lead for DTE or
‘
C
’
lead for DCE; a low level
on CTS* is interpreted as an ON condition and a high level as an OFF condition.
Bit 7
Lead value
0 = Off
1 = On
Bits 6:4
Special character detect
This indication occurs if two consecutive characters matching the value indicated in
the table below are received:
Bit 3
Overrun error
The OE bit indicates that the receiver buffer and FIFO have been overrun. At least
one new character has been received, but lost since there was no room available in
Register Name: RISRl
Register Description: Receive Interrupt Status Register - Low
Default Value: x
’
00
Access: Byte Read/Write
Intel Hex Address: x
’
8A
Motorola Hex Address: x
’
89
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
LVal
SCDET2
SCDET1
SCDET0
OE
PE
0
LChg
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Binary Value for Timer
SCdet[2:0]
Status
000
None detected
001
Matched the value in SCHR1
010
Matched the value in SCHR2
011
Matched the value in SCHR3
100
All
‘
0
’
condition
101
All
‘
1
’
condition
110
Alternating
‘
0
’
and
‘
1
’
condition
111
SYN detect