Blackmagic Design URSA Mini Pro 12K (PL) - Manual (Page 278)

Slave devices pass through the tally packet on their output and update the monitor tally status,
so that monitor devices connected to that individual output may display tally status without
knowledge of the device id they are monitoring.
Assumptions
Any data alignment / padding is explicit in the protocol. Bit fields are packed from LSB first.
Blanking Encoding
One tally control packet may be sent per video frame. Packets are encoded as a SMPTE 291M
packet with DID/SDID x51/x52 in the active region of VANC line 15. A tally control packet may
contain up to 256 bytes of tally information.
Packet Format
Each tally status consists of 4 bits of information:
uint4
bit 0: program tally status (0=off, 1=on)
bit 1: preview tally status (0=off, 1=on)
bit 2-3: reserved (0x0)
The first byte of the tally packet contains the monitor device tally status and a version number.
Subsequent bytes of the tally packet contain tally status for pairs of slave devices. The master
device sends tally status for the number of devices configured/supported, up to a
maximum of 510.
struct tally
uint8
bit 0: monitor device program tally status (0=off, 1=on)
bit 1: monitor device preview tally status (0=off, 1=on)
bit 2-3: reserved (0b00)
bit 4-7: protocol version (0b0000)
uint8[0]
bit 0: slave device 1 program tally status (0=off, 1=on)
bit 1: slave device 1 device preview tally status (0=off, 1=on)
bit 2-3: reserved (0b00)
bit 4: slave device 2 program tally status (0=off, 1=on)
bit 5: slave device 2 preview tally status (0=off, 1=on)
bit 6-7: reserved (0b00)
uint8[1]
bit 0: slave device 3 program tally status (0=off, 1=on)
bit 1: slave device 3 device preview tally status (0=off, 1=on)
bit 2-3: reserved (0b00)
bit 4: slave device 4 program tally status (0=off, 1=on)
bit 5: slave device 4 preview tally status (0=off, 1=on)
bit 6-7: reserved (0b00)
. . .
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