Only three bits of the Connection Memory High are useful, bits CMHb2, CMHb1 and CMHb0. The other fivebits are read as zeroes, and are not changeable. When CMHb0 is a logical ‘0’ the output channel associated withthe Connection Memory High location is placed into a high impedance state. When CMHb0 is set to a logical‘1’, the output channel driver is turned on and information from either Data Memory (switched mode) orConnection Memory Low (Message mode) is placed on the output. CMHb1 controls the state of the bit on theCSTo output that is associated with that particular Connection Memory

High location and channel. This bit is not used in the MT8981. CMHb2 is the channel’s mode control bit. When CMHb2 is a logical

‘0’, the associated output channel is placed into Switching mode and the contents of the Data Memory location addressed by Connection Memory Low are output on the channel. When CMHb2 is a logical ‘1’, the output channel is in Message mode and the contents of Connection Memory Low are placed on the output channel.