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Lexicon, Inc.
RV-8 Serial Communications Protocol
5.4 RV8 Receive Buffer
The RV8 has an internal receive buffer. The buffer is 256 Bytes and will transmit a NAK packet with an
error code of DC_ERR_BUFFER_FULL to the HOST if the buffer is full. If the buffer is full, all data
transmitted to the RV8 will be ignored. Therefore, making the currently transmitted packet, if partially
transmitted invalid.
5.5 RV8 Hardware Verification
This test verifies the RS232 ports are working by comparing the transmitted signal (at pin 2) to the received
signal (at pin 3). The RV8 transmits a known test signal just following a power up. The RV8 monitors the
serial port receivers while transmitting the test signal. If the signals are the same, the test passes. In order to
test this circuit, RS232 Wraparound plug(s) are needed and must be installed at the female D9 connector(s)
on the rear panel of the RV8 labeled "RS232". The wraparound plug shorts pins 2 to 3, allowing for the
RV8 to receive the signal it is transmitting. Once installed, power cycle the RV8 and verify the following
message is displayed on the FPD:
This message is displayed for about 2 seconds before entering normal operating mode. If no messages are
displayed, then both wrap tests failed.
6 Data Link Layer
The data link layer is used to define a transmission packet. The layer appends a header and tail that
encloses the transmitted application packet data. The data link header will contain the start of packet byte
and count of bytes to follow. The data link tail will contain the end of packet byte.
Data Link Header:
Byte Number
Description
First Byte(0)
Start of Packet (SOP)
Byte(1)
DLL Data Count
Application Header:
Byte(2)
Command
APP Data Count (number of application data bytes to
Byte(3)
Follow)
Application Data:
Byte(4)
Data[0]
Byte(5)
Data[1]
...
Data[...]
Last Data Byte -1
Data[Data Count -1]
Data Link Tail:
Last Byte
End of Packet (EOP)
6.1 Errors
If the number of DLL data bytes received is the same as the data count and an EOP has not been received,
the RV8 responds by transmitting a NAK packet with an error code DC_ERR_INVALID_PACKET. The
RV8 then continues to look for a SOP byte and will not process the erroneous application packet. The
HOST can use this as an indicator to retransmit the corrupted packet.
© 2004 Lexicon, Inc. All rights reserved.
SERIAL PORT A PASSED
SERIAL PORT B PASSED
Printed on: 01/18/05
Value
0xF1
nn
nn
nn
nn
nn
nn
nn
0xF2
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