Embedded Solutions
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generated one, adding a post amble pattern etc. Please refer to the register bit
definitions for more details.
DATA IN/OUT
0
1
0
0
0
1
1
0
1
1
0
1
0
MANCHESTER ENCODING
FIGURE 5
PMC BISERIAL III HW2 MANCHESTER TIMING DIAGRAM
The receive function uses a free running shift register coupled with the receive state-
machine to capture the data. When the receiver detects the idle pattern followed by 4
Manchester ‘0’s the receiver starts to capture data. The data is read in and stored into
the DPR. The embedded length is used to determine where the CRC should be. The
CRC is calculated as the data is received and checked against the CRC received with
the packet. An error bit is set if the two do not match. Manchester errors within the
packet are detected, and used to abort processing of the message. After a packet has
been received the Post Amble is tested to see that it follows the proper protocol. The
Manchester and Post Amble errors are also latched in status bits.
This document is somewhat restricted as to the technical content allowed in describing
the electrical interface. The document “Point-to-Point Data Bus Protocol Specification –
C72-1199-069” provides a more complete description of the interface.
The PMC BiSerial-III-HW2 also supports an SDLC interface. This is a synchronous
interface with separate clock and data inputs and outputs. Each message is delimited
by start/stop flag characters consisting of an eight-bit (0x7E) pattern. In order to avoid
false flag detection from the data pattern, if five consecutive ones appear anywhere in
the data stream, an additional zero is inserted to avoid having six consecutive one bits.
On the receive side, when five ones are received the sixth bit is monitored. If it is a
zero, it is removed from the data stream, if it is a one then either a start/stop flag or an
abort character (0xFE) has been detected.
To send a message, write the message data to the transmit DPRs, specify the start and
stop addresses and configuration control bits, then enable the transmitter. The state-
