aluVoiceSignalBitsState is an array of two bytes used to indicate the current state of the ABCD signalling bits for the voice channel. The first byte of the array describes the RX ABCD bits. The second byte of the array describes the TX ABCD bits. The byte arrangement is as follows: array index: | 0 1 | | RX TX | Each byte carries ABCD bits in the least significant nibble. The byte's most significant bit indicates the validity of the ABCD bits. The bit arrangement is as follows: bit pos: | 7 6 5 4 3 2 1 0 | | V x x x A B C D | 'V' - validity (0 = invalid, 1 = valid) 'x' - don't care ABCD bits are marked invalid for a variety of situations (eg. channel-group not configured, channel status not up, etc.).