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File name cd changer protocol.pdf

Page 1 of 13 Blaupunkt ( DMS ?? ) for controlling a Blaupunkt car radio. It is basically a 2 wire (rx/tx) async. serial protocol with 9 bits of data where the 8th bit is used for synchronisation. That made it easy to interface it to a player or PC because you can use the serial port. The only documents that're left is one sheet of paper containing the initial communication between a cd changer and the radio and the source code. Here is the protocol cut: radio baudrate 4800 0x17B 0x17C 0x17D 0x17E 0x17F 0x180 0x48 0x02 0x14F 0x180 0x9F 0x14F 0x180 0xA1 0x14F 0x180 0xAD 0x14F 0x180 0x48 0x01 0x14F 0x10F 0x48 0x01 0x14F 0x103 (3 times ) -> (3 times ) -> (3 times ) -> (3 times ) -> (3 times ) -> -> -> -> direction,info changer no response no response no response no response no response 0x180 0x48 0x02 no response 0x180 0x9F no response 0x180 0xA1 no response 0x180 0xAD no response 0x180 0x48 0x01 no response 0x10F 0x48 0x01 0x14F 0x103 ->, change in baudrate to 9600 -> -> -> -> -> -> -> -> -> -> -> -> -> <<<<<- 10/07/2006 Page 2 of 13 0x20 0x09 0x20 0x00 0x14F 0x10B 0x20 0x14F 0x101 0x09 0x01 0x14F 0x10D 0x01 0x09 0x43 0x57 0x14F <<<<<<-( text info ??? ) <- (8 times space ) <<-( disc / track info ??? ) <<<<- ( disc / track / time info ( BCD ) ?? ) <<<<<- 0x20 0x09 0x20 0x00 0x14F 0x10B 0x20 0x14F 0x101 0x09 0x01 0x14F 0x10D 0x01 0x09 0x43 0x57 0x14F Kenwood The protocoll used here is a synchron serial protocoll. First let us start with the connector pinout. The pins have a 2.54mm distance, so you can simply build a plug using some prototyping board ... New connector pin-out (for head units >'99?) Thanks to Patrick Loef for this information. pin 1 2 3 4 5 6 7 8 direction description O O I O I CH-REQH - Request output to changer; "Low" : Request Ground Vcc +12V CH-CON - Changer control; "High" : Operation mode "Low" : Standby CH-MUTE - Mute request from changer; "High" : Mute AGND - Audio Ground CH-RST - Reset output to changer Audio right channel 10/07/2006 Page 3 of 13 9 10 11 12 13 I I O I I/O CH-REQC - Request input from changer; "Low" : Request CH-DATAC - Data input from changer CH-DATAH - Data output to changer Audio left channel CH_CLK - Clock input/output for changer The following works only with newer kenwood radios. Older models have the same pinout but use some more simple protocol ... The clock low and high periods had a length of 4us. The data is transfered in bytes ( 8 bits ... MSB first ), data is valid at the rising clock edge.. The data transfer is initiated either by the radio or the changer, the initiator just pulls its fs line low. When the changer starts the communication it gets 40 clocks from the radio ( 4 bytes addr + 1byte data size ). The radio then sets its fs to low if it accepts the transfer. When a transfer is initiated by the radio by setting its fs low it waits for the changer to answer with a low fs, then it sends the 4 byte addr header, the size byte for the data and the data. Packet header,