CD1865 Datasheet, PDF (109/150 Pages) Intel Corporation – Intelligent Eight-Channel Communications Controller

Intelligent Eight-Channel Communications Controller — CD1865
Bit
Bits 7:4
Description
Reserved, must be a ‘0’.
Specifies the number of Good Data bytes for transfer from the Receive FIFO at the time of service request.
This may be larger or smaller than the threshold level set by the user. This register reflects the actual amount
of data available, which can be greater than the threshold level if service-request response is slow, or less
than the threshold if some other event (such as an error condition) has caused the Receive Good Data
Interrupt. This register need only be read when receiving Good Data; by default all exceptions are one
character, and the value in this register during a Receive Exception is not defined or meaningful. The RDCR
contains a zero if the current service request is for the NNDT case.
Bits 3:0
C3
C2
C1
C0
Number of Good Bytes
0
0
0
0 Does not occur
0
0
0
11
0
0
1
02
0
0
1
13
0
1
0
04
0
1
0
15
0
1
1
06
0
1
1
17
1
0
0
08
1001 to 1111
Does not occur
9.3.2
Receive Data Register
Register Name:
Register Description: Receive Data Register
Default Value: 0
Access: Read Only
Bit 7
Bit 6
Bit 5
D7
D6
D5
Bit 4
D4
Bit 3
D3
Bit 2
D2
8-Bit Hex Address: $78
Intel Hex Address: $F0
Motorola Hex Address: $F1
Bit 1
Bit 0
D1
D0
This register accesses the Receive Data FIFO for the channel. It is used by all channels to transfer
Receive FIFO data to the host. Successive reads transfer bytes from the FIFO to the host. Reading
this register increments an internal pointer to the Data and Status FIFOs. During service-request
routines for Good Data, this is the only register that must be read. During service-request routines
for Receive Exception, the Receive Status register must be read first, then this register may be read.
If both the RCSR and this register are to be read, the RCSR must be read first because reading this
register causes the FIFOs to ‘pop’.
Any attempt to write to this register causes unpredictable results.
Datasheet
109