
CD1865
—
Intelligent Eight-Channel Communications Controller
110
Datasheet
9.3.3
Receive Character Status Register
This register accesses the status information for the current receive character.
Multiple errors in 1 byte are possible because the CD1865 evaluates the character bit-by-bit as it
receives it. For example, a parity error is detected and flagged before a framing error. If a character
is received with every bit (including the stop bit) equal to a
‘
0
’
, it is marked as a line-break. If some
bits are a
‘
1
’
, but the Stop bit is
‘
missing
’
a
‘
0
’
, it is marked as a framing error. If odd parity is set
and the bits received are all zeroes, it is marked as both a break character and a parity error. In
addition to any other bits, the Overrun bit is set if an overrun has occurred. Any attempt to write to
this register causes unpredictable results.
Register Name:
Register Description: Receive Character Status Register
Default Value: 0
Access: Read Only
Bit 7
Bit 6
8-Bit Hex Address: $7A
Intel Hex Address: $F4
Motorola Hex Address: $F5
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Time-out
SC Det2
SC Det1
SC Det0
Break
PE
FE
OE
Bit
Description
Bit 7
Time-out:
Indicates that the Receive FIFO is empty, and no data has been received within the receive time-
out period. There is no data character associated with this status and no other status bits are valid if the Time-
out bit is set. Must be
‘
armed
’
by the NNDT bit in .
Bits 6:4
Special Character Detect (SCD0-2):
NOTE:
No special-character match is performed if any type of error occurs. The second character of a two-
character sequence cannot cause a receiver overrun.
Bit 3
Break:
Indicates that a break has been detected.
Bit 2
Parity Error:
Indicates that a parity error has been detected.
Bit 1
Framing Error:
Indicates that a bad Stop bit has been detected.
Bit 0
Overrun Error:
Indicates that new data has arrived but the CD1865 FIFO and Holding registers
are full. The new data is lost and the overrun indication is flagged on the last character received
before the overrun occurred.
SCD2
SCD1
SCD0
Status
0
0
0
None detected
0
0
1
Special Character 1 or Special Character 1 and 3 sequence matched
(only if Special Character 1 and 3 sequence is enabled).
0
1
0
Special Character 2 or Special Character 2 and 4 sequence matched
(only if Special Character 1 and 3 sequence is enabled).
0
1
1
Special Character 3 (only if Special Character 1 and 3 sequence is not
enabled).
1
0
0
Special Character 4 (only if Special Character 2 and 4 sequence is not
enabled).