Block Transfer Operations (PDF 15K).
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1. 718 interface the header byte s and the data to be transmitted e The AVT 718 interface receives the header byte s and data from the host e The AVT 718 interface buffers the data and checks the byte count e The AVT 718 interface transmits the data onto the network e The AVT 718 interface echoes the received block and or reports status Note This method is much simpler to use than the Block Specific method No other commands or specific sequence of events are required The AVT 718 interface checks the length of the message to be transmitted and handles it accordingly The host does not need to tell the AVT 718 interface if it is a block or not Commands There are three forms the host can use to command the AVT 718 to transmit a message or data They are described here in the User s Manual and in the document titled Long Messages Alternate Header Formats Normal Format If the message is 15 bytes or less then the normal format may be used Ox aa bb cc x count of bytes to follow message bytes aa bb cc message bytes Example 05 81 F1 Cl 48 9B Alternate Format 1 If the message byte count is 16 to 255 inclusive alternate format 1 is available The header byte is 11 which indicates that one length byte follows The data then follows 11 xx aabbcc 11 header byte xx count of bytes to follow aa bb cc message bytes Advanced Vehicle Technologies Inc Page 2 Alternat2. AI ADVANCED VEHICLE TECHNOLOGIES Inc 19 October 2002 All numbers are Hex The J1850 specification does not support the transfer of more than 11 bytes of data plus CRC at one time However there are times where it is desirable to transmit a block data greater than 11 bytes Such as GM s Class 2 block download and block upload capabilities Several AVT interfaces support this function in VPW mode only in both regular speed and high speed modes This is a summary of how to use the block data transfer functions The terms download and upload are not used here In this paper block transfers are relative to the AVT interface Block transfers are either transmit onto the VPW bus or receive from the VPW bus There are two methods by which the host computer can send a block of data e Short Method or Transmit Command method e Block Specific method The AVT 718 interface supports both methods The AVT 716 921 and 931 interfaces only support the Block Specific Method All AVT interfaces only support the receive method described in this document 1509 Manor View Road Davidsonville MD 21035 USA 1 410 798 4038 voice 1 410 798 4308 fax http www avt hq com support avt hq com Transmit a Block Short Method This method only applies to the AVT 718 interface The Short or Transmit Command method is an extension of the normal transmit command The sequence of events is e Host sends the AVT
3. e Format 2 If the message byte count is between 256 and 8192 inclusive alternate format 2 is available The header byte is 12 which indicates that two length bytes follow The data then follows 12 xx yy aabbcc 12 header byte xx count of bytes to follow most significant byte yy count of bytes to follow least significant byte aa bb cc message bytes Usage All three formats are compatible and may be used as desired For example the host wants to transmit the following message onto the bus Al B2 C3 D4 E5 F6 A7 B8 C9 DA EB FC AD BE Example The following messages from the host to the AVT 718 interface are equivalent The header byte s are bold and underlined for clarity OE A1 B2 C3 D4 E5 F6 A7 B8 C9 DA EB FC AD BE 11 0E A1 B2 C3 D4 E5 F6 A7 B8 C9 DA EB FC AD BE 12 00 0E A1 B2 C3 D4 E5 F6 A7 B8 C9 DA EB FC AD BE Note The AVT 718 supports a maximum transmit block size of 8192 bytes 8 KBytes 2000 Commands to the Host for Block Transmit The AVT 718 supports the following commands associated with receiving a transmitted block 52 21 00 Echo the transmitted block Default The entire transmitted block is echoed to the host as it is received 52 21 O1 Do not echo the transmitted block Only the status message transmit acknowledgment is sent to the host 52 40 00 Disable transmit acknowledgments 52 40 01 Enable transmit acknowledgments Default Advanced Vehicle Technologies Inc Page 3 E
4. ion The default mode is no echo disabled This means any block sent by the host will be echoed back to the host Sending the command 52 21 01 will enable the no echo feature When enabled the received block is not echoed back to the host Host sends 53 20 xx yy to the AVT interface AVT interface responds with 62 20 01 Host sends data block to the AVT interface AVT interface sends a 03 header byte AVT interface sends the receive status byte AVT interface sends a two byte value of message byte count gt gt gt gt gt AVT interface sends 62 20 00 to the host Advanced Vehicle Technologies Inc Page 7
5. ize in a Class 2 Mode 36 message The byte count in the 53 command is the total length of the message including all header type count data and CRC bytes as defined in the Mode 36 message e Receive the response 62 20 01 which indicates that the AVT interface has entered block transfer mode and it is ready to receive the data block from the host e Within 3 seconds the host must begin to send the data block to the AVT interface e There must not be more than approximately 256 microseconds between consecutive bytes 64 microseconds when in high speed mode This minimum time will vary depending on how bytes are passed by the host to the interface and other factors Not applicable to the AVT 718 interface e The AVT interface will receive the same data block it is sending it will be passed to the host Refer to the receive description below This echo can be shut off by using the 52 21 01 command which enables the no echo feature The command 52 21 00 disables the no echo feature thus the transmitted block is echoed back to the host this is the default e When all the data has been sent to the interface and all the data has been received from the bus the interface will respond with 62 20 00 to indicate that it has exited the block transfer mode Example Command 5 20 xx yy Response 62 20 01 E Advanced Vehicle Technologies Inc Page 5 Receive a Block e No operator action is required to
6. nterface AVT interface responds with 62 20 01 Host sends data block to the AVT interface AVT interface sends FO to the host AVT interface sends the received data block AVT interface sends the receive status byte AVT interface sends a two byte value of message byte count AVT interface sends fifteen 15 FO bytes AVT interface sends 62 20 00 to the host E Advanced Vehicle Technologies Inc Page 6 Error Condition and Notification If the interface realizes that an error has occurred e g the 3 seconds time out the interface will respond with the error message 21 32 A 62 20 00 message exit from block transfer mode will follow Example Host sends 52 2001 Command block mode gt Interface responds 62 2001 Block mode entry acknowledged gt Error occurs host delays sending data Interface responds 21 32 Block mode error Interface responds 62 2000 Block mode exited There is an error that may occur during a block transmit operation If the interface does not receive a byte for transmission within the allowable time the VPW bus will experience a time out EOD and the block transfer will abort early The AVT interface should detect this and will read the remaining bytes from the host discard them send the error message 21 32 to the host and exit block mode 62 20 00 No Echo Mode Enabled A no echo feature is included with the block transfer funct
7. prepare the AVT interface to receive a block of data Ifa block transfer commences on the bus at the same speed the interface is set for the block will be received and forwarded to the host e When block transfer starts the AVT interface will send the host an FO byte to indicate that a block of data will follow Note The AVT interface has no advance information about the size of the incoming block Thus it can only send an FO to indicate that reception of a block has started The host must be able to handle this e Immediately following the FO byte will be the block of data e The receive status byte is appended to the end of the data block e The received block byte count a two byte value high byte low byte will follow the status byte The byte count will NOT include the status byte the status byte is not part of the message received e A total of fifteen 15 FO bytes are appended These serve to indicate the end of the block e The AVT interface exits block receive mode If in high speed mode the interface stays in high speed mode Examples Receive a Block AVT interface sends FO to the host AVT interface sends the received data block to the host AVT interface sends the receive status byte to the host AVT interface sends a two byte value of message byte count AVT interface sends fifteen 15 FO bytes to the host Transmit a Block u Host sends 53 20 xx yy to the AVT i
8. xplanations 52 20 00 the 52 40 xx command is irrelevant Transmit a block of data Host receives from the AVT 718 the following FO gg hh kk pp ss mm nn FO FO FO FO FO FO FO FO FO FO FO FO FO FO FO The first FO indicates the start of a block being received gg hh kk pp are the actual block data bytes oe 99 ss is the received status byte 60 indicates transmitted successfully with no errors mm nn is the count of received data bytes only The fifteen FO bytes signal the end of the block 52 2001 and 524001 Transmit a block of data Host receives from the AVT 718 the following F3 ss mm nn F3 indicates a block transmit report 3 bytes follow oe 29 ss is the received status byte 60 indicates transmitted successfully with no errors mm nn is the count of received data bytes only 522001 and 52 40 00 Transmit a block of data The AVT 718 does not reply at all to the host Receiving a block The AVT 718 receives a block of data the same as the other AVT interface units That method is described later in this document Advanced Vehicle Technologies Inc Page 4 Transmit a Block Block Specific Method e Send the command 53 20 xx yy to the AVT interface e The bytes xx and yy are high and low order bytes respectively of the byte count of the block of data to be transmitted NOTE Do not confuse the byte count in the 53 command with the block s
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