Datasheet

DS21352/DS21552
94 of 137
17. PROGRAMMABLE IN–BAND LOOP CODE GENERATION AND
DETECTION
Each framer in the DS21352/552 has the ability to generate and detect a repeating bit pattern that is from
one to eight bits in length. To transmit a pattern, the user will load the pattern to be sent into the Transmit
Code Definition (TCD) register and select the proper length of the pattern by setting the TC0 and TC1
bits in the In–Band Code Control (IBCC) register. Once this is accomplished, the pattern will be
transmitted as long as the TLOOP control bit (CCR3.1) is enabled. Normally (unless the transmit
formatter is programmed to not insert the F–bit position) the framer will overwrite the repeating pattern
once every 193 bits to allow the F–bit position to be sent. As an example, if the user wished to transmit
the standard “loop up” code for Channel Service Units which is a repeating pattern of ...10000100001...
then 80h would be loaded into TDR and the length would set to 5 bits.
Each framer can detect two separate repeating patterns to allow for both a “loop up” code and a “loop
down” code to be detected. The user will program the codes to be detected in the Receive Up Code
Definition (RUPCD) register and the Receive Down Code Definition (RDNCD) register and the length of
each pattern will be selected via the IBCC register. The framer will detect repeating pattern codes in both
framed and unframed circumstances with bit error rates as high as 10E–2. The code detector has a
nominal integration period of 48 ms. Hence, after about 48 ms of receiving either code, the proper status
bit (LUP at SR1.7 and LDN at SR1.6) will be set to a one. Normally codes are sent for a period of 5
seconds. it is recommend that the software poll the framer every 100 ms to 1000 ms until 5 seconds has
elapsed to insure that the code is continuously present.
IBCC: IN–BAND CODE CONTROL REGISTER (Address=12 Hex)
(MSB) (LSB)
TC1 TC0 RUP2 RUP1 RUP0 RDN2 RDN1 RDN0
SYMBOL POSITION NAME AND DESCRIPTION
TC1 IBCC.7 Transmit Code Length Definition Bit 1. See Table 17-1
TC0 IBCC.6 Transmit Code Length Definition Bit 0. See Table 17-1
RUP2 IBCC.5 Receive Up Code Length Definition Bit 2. See Table 17-2
RUP1 IBCC.4 Receive Up Code Length Definition Bit 1. See Table 17-2
RUP0 IBCC.3 Receive Up Code Length Definition Bit 0. See Table 17-2
RDN2 IBCC.2 Receive Down Code Length Definition Bit 2. See Table 17-2
RDN1 IBCC.1 Receive Down Code Length Definition Bit 1. See Table 17-2
RDN0 IBCC.0 Receive Down Code Length Definition Bit 0. See Table 17-2