Denon DCM-5001 Serial Protocol - Page 4

.3 Command format and answer format This unit shall be based on commands each of which consists of a data row ( some commands are without a PC ) composed of command codes ( CC ) and parameter codes ( PC ). The transmitting station shall be designed to send block check characters ( BCC ) following ETX, with the data row enclosed in STX ( text start 02h ) and ETX ( text termination 03h ). The receiving station shall regard receipt of BCC as the completion of command reception when it has received STX. Here are the formats. Commands STX Start of Text 02h CC Command Code Command code PC Parameter Code Defined for each command ( contents and number of parameters ) ETX End of Text 03h BCC Block Check Character CC + PC0 + PC1 + PC2 + + PCn + ETX = Xyh (Each of X and Y is 4 bits long ) X , Y=0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F BCCH ( high-level byte ) = X as converted to an ASCII code BCCL ( low-level byte ) = Y as converted to an ASCII code Answers STX Start of Text 02h RC Reply Code Reply code(=Command code) AC Answer Code Answer code PC Parameter Code Defined for each command ( contents and number of parameters ) ETX End of Text 03h BCC Block Check Character CC + PC0 + PC1 + PC2 + + PCn + ETX = Xyh (Each of X and Y is 4 bits long) X , Y=0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F BCCH ( high-level byte ) = X as converted to an ASCII code BCCL ( low-level byte ) = Y as converted to an ASCII code .4 Protocol for data transmission and reception This unit is based on half-duplex communication. The unit shall therefore transmit commands and receive answers according to the following procedure. .1 Basic procedure The host shall select commands for this unit and transmit them to this unit. Having issued a command, the host shall receive an answer from this unit, then issue the next command. The host shall analyze the RC, AC, and PC as answers given and decide whether the command has been normally executed. The host shall give an answer to a command that gives operational instructions, then issue a status request command, and decide whether this unit has finished operating with regard to the command that gives operational instructions. The time from the start of command transmission to the end of command transmission should be max 40 msec. The time from the completion of command transmission to the start of answer-back is 40 msec ( max ). This unit cannot receive any commands for about 15 seconds after the power switch is turned on. .2 Communication errors Having received a command, which results in a communication error ( overrun, framing, or parity error ), this unit shall give NAK ( 15h ). ( MAX 80ms from the start of command transmission ) If the host has received NAK from this unit, it shall retransmit the command that it has transmitted immediately beforehand. Having received an answer, which results in a communication error ( overrun, framing, or parity error ), the host shall respond with NAK. If it has received NAK from the host, this unit shall retransmit the answer it has transmitted immediately beforehand. ( MAX 40ms) When there is no answer from the unit within 80 ms, the host shall retransmit the command.