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20. T1 BIT ORIENTED CODE (BOC) CONTROLLER
The DS21Q55 contains a BOC generator on the transmit side and a BOC detector on the receive side. The
BOC function is available only in T1 mode.
20.1 Transmit BOC
Bits 0 through 5 in the TFDL register contain the BOC message to be transmitted. Setting BOCC.0 = 1
causes the transmit BOC controller to immediately begin inserting the BOC sequence into the FDL bit
position. The transmit BOC controller automatically provides the abort sequence. BOC messages will be
transmitted as long as BOCC.0 is set.
To transmit a BOC, use the following:
1) Write 6-bit code into the TFDL register.
2) Set SBOC bit in BOCC register = 1.
20.2 Receive BOC
The receive BOC function is enabled by setting BOCC.4 = 1. The RFDL register will now operate as the
receive BOC message and information register. The lower six bits of the RFDL register (BOC message
bits) are preset to all ones. When the BOC bits change state, the BOC change of state indicator, SR8.0
will alert the host. The host will then read the RFDL register to get the BOC message. A change of state
will occur when either a new BOC code has been present for time determined by the receive BOC filter
bits, RBF0 and RBF1, in the BOCC register.
To receive a BOC, use the following:
1) Set integration time via BOCC.1 and BOCC.2.
2) Enable the receive BOC function (BOCC.4 = 1).
3) Enable interrupt (IMR8.0 = 1).
4) Wait for interrupt to occur.
5) Read the RFDL register.
6) The lower six bits of the RFDL register is the message.