MC68HC58
CONTROL AND STATUS CODES
MOTOROLA
TECHNICAL DATA
5-9
All information in the status byte is frozen while CS is asserted, and updated when CS
is negated.
5.3.1 RFS[7:5] — Receive FIFO Status Field
This bit field shows the status of the RxFIFO buffer. When interrupts are enabled, RFS
can be used to determine the source of an interrupt request. Table 5-5 shows the
RxFIFO status encoding field. In the DLC, when the RFS bit field indicates that a com-
pletion code is at the head of the buffer, the accompanying data byte contains that
same completion code.
5.3.1.1 Buffer Invalid or Empty
This value indicates that the accompanying data byte is not valid because the RxFIFO
buffer is empty or a flush frame command is being executed.
5.3.1.2 Buffer Contains More Than One Byte
This value indicates that the RxFIFO buffer contains two to 12 bytes of data and no
completion code.
5.3.1.3 Buffer Contains a Completion Code
This value indicates that the RxFIFO buffer contains both data bytes and a completion
code. The completion code is not at the head of the buffer.
5.3.1.4 Thirteenth Byte Received
This value indicates that the RxFIFO buffer contains 12 bytes and a 13th byte has
been received. There is no completion code in the buffer.
SBR — Status Byte Register
7
6
5
4
3
2
1
0
RFS
DLI
NETF
4XMD
TMFS
RESET:
0
X
0
Table 5-5 RFS Field Encoding
Value
Description
000
Buffer invalid or empty
001
Buffer contains more than one byte
010
Buffer contains a completion code
011
Data byte in 13th buffer position, no completion code
100
One data byte in buffer
101
Completion code at head of buffer, more bytes available
110
Completion code at head of buffer, another frame available
111
Completion code only at head of buffer