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PEB 20550
PEF 20550
Operational Description
Semiconductor Group
102
01.96
3.6.3
In receive direction 2
×
32-byte FIFO-buffers (receive pools) are also provided for each
channel. There are two different interrupt indications concerned with the reception of
data:
– A RPF (Receive Pool Full) interrupt indicates that a 32-byte block of data can be read
from the RFIFO with the received message not yet complete.
– A RME (Receive Message End) interrupt indicates that the reception of one message
is completed, i.e. either
– one message with less than 32 bytes, or the
– last part of a message with more than 32 bytes
is stored in the CPU accessible part of the RFIFO.
The CPU must handle the RPF-interrupt before additional 32 bytes are received via the
serial interface, as failure to do so causes a RDO (Receive Data Overflow).
Status information about the received frame is appended to the frame in the RFIFO. This
status information follows the format of the RSTA-register, unless using the SACCO-A
in clock mode 3. The CPU can read the length of the received message (including the
appended Receive Status byte) from the RBCH- and RBCL-registers.
After the received data has been read from the RFIFO, this must be explicitly
acknowledged by the CPU issuing a RMC- (Receive Message Complete)
command!
The following figure gives an example of an interrupt controlled reception sequence,
supposing that a long frame (66 bytes) followed by a short frame (6 bytes) are received.
Data Reception in Interrupt Mode
Figure 52
Interrupt Driven Reception Example
ITD05849
6
2
32
32
Receive 66 Bytes
Receive
6 Bytes
RMC
RME
Byte
Count
Serial
Interface
SACCO
CPU
Interface
RME
RFIFO
7 Bytes
RMC
3 Bytes
RFIFO
Count
Byte
RPF
RPF
RFIFO
32 Bytes
RFIFO
32 Bytes
RMC
RMC