DCC
DCC Commands
Two type of commands, raw DCC instructions and programming track instructions.
Programming Track Instructions
61 Read CV (QCVS)
Format: <61><Low CV#><High CV#><Mode>
- <Dat1> is the MSB # of the CV read (supports CVs 1 - 65536)
- <Dat2> is the LSB # of the CV read
- <Dat3> is the programming mode to be used
This command is used exclusively with service mode. Sent by the cab to the command station in order to read a CV value. The command station shall respond with a PCVS message containing the value read, or NAK if the CV cannot be read.
62 Report CV (PCVS)
Format: <62><Low CV#><High CV#><Val>
- <Dat1> is the MSB # of the CV read (supports CVs 1 - 65536)
- <Dat2> is the LSB # of the CV read
- <Dat3> is the read value
This command is used exclusively with service mode. Sent by the command station to report a read CV.
81 Write CV in Service mode (WCVS)
Format: <81><Low CV#><High CV#><Mode><Val>
- <Dat1> is the MSB # of the CV to be written (supports CVs 1 - 65536)
- <Dat2> is the LSB # of the CV to be written
- <Dat3> is the service write mode
- <Dat4> is the value to be written
Sent to the command station to write a DCC CV in service mode.
82 Write CV (byte) in Ops Mode (WCVO)
Format: <82><Session><High CV#><Low CV#><Val>
- <Dat1> is the session number of the loco to be written to
- <Dat2> is the MSB # of the CV to be written (supports CVs 1 -65536)
- <Dat3> is the LSB # of the CV to be written
- <Dat4> is the value to be written
Sent to the command station to write a DCC CV in OPS mode to specific loco.(on the main)
83 Write CV (bit) in Ops Mode (WCVB)
Format: <83><Session><High CV#><Low CV#><Val>
- <Dat1> is the session number of the loco to be written to
- <Dat2> is the MSB # of the CV to be written (supports CVs 1 -65536)
- <Dat3> is the LSB # of the CV to be written
- <Dat4> is the value to be written
The format of Dat4 is that specified in NMRA RP9.2.1 for OTM bit manipulation in a DCC packet. This is '111CDBBB' where C is 1 for write, D is the bit value and BBB is the bit number.
Sent to the command station to write a DCC CV in OPS mode to specific loco.(on the main)
Raw DCC Instructions
These are CBUS packets which contain a preformatted DCC command, typically used for accessory operation or programming on main. The last byte of each DCC packet is the error check, so it's not actually necessary as the command station can complete it.
- The <REP> byte is a 6 bit count of the number of times the command is sent to the track.
- Bit 7 is used for an operational mode write when the command has to be sent to the same address twice.
- Bit 6 is used allow a deactivate command to follow an activate command.
80 Request 3-byte DCC Packet (RDCC3)
Format: <80><REP><Byte0>..<Byte2>
- <Dat1(REP)> is # of repetitions in sending the packet.
- <Dat2>..<Dat4> 3 bytes of the DCC packet.
Allows a device to request a 3 byte DCC packet to be sent to the track. The packet is sent <REP> times and is not refreshed on a regular basis.
A0 Request 4-byte DCC Packet (RDCC4)
Format: <A0><REP><Byte0>..<Byte3>
- <Dat1(REP)> is # of repetitions in sending the packet.
- <Dat2>..<Dat5> 4 bytes of the DCC packet.
Allows a device to request a 4 byte DCC packet to be sent to the track. The packet is sent <REP> times and is not refreshed on a regular basis.
C0 Request 5-byte DCC Packet (RDCC5)
Format: <C0><REP><Byte0>..<Byte4>
- <Dat1(REP)> is # of repetitions in sending the packet.
- <Dat2>..<Dat6> 5 bytes of the DCC packet.
Allows a device to request a 5 byte DCC packet to be sent to the track. The packet is sent <REP> times and is not refreshed on a regular basis.
E0 Request 6-byte DCC Packet (RDCC6)
Format: <E0><REP><Byte0>..<Byte5>
- <Dat1(REP)> is # of repetitions in sending the packet.
- <Dat2>..<Dat7> 6 bytes of the DCC packet.
Allows a device to request a 6 byte DCC packet to be sent to the track. The packet is sent <REP> times and is not refreshed on a regular basis.
