Datasheet

DS2148/DS21Q48
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6 DIAGNOSTICS
6.1 In-Band Loop Code Generation and Detection
The DS2148 can generate and detect a repeating bit pattern that is from one to eight or sixteen bits in
length. To transmit a pattern, the user will load the pattern to be sent into the Transmit Code Definition
(TCD1 and TCD2) registers and select the proper length of the pattern by setting the TC0 and TC1 bits in
the In-Band Code Control (IBCC) register. When generating a 1, 2, 4, 8, or 16 bit pattern both the
transmit code registers (TCD1 and TCD2) must be filled with the proper code. Generation of a 1, 3, 5, or
7-bit pattern only requires TCD1 to be filled. Once this is accomplished, the pattern will be transmitted as
long as the TLCE control bit (CCR3.3) is enabled. 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 TCD1 and the length would set using TC1 and TC0 in the IBCC register to 5
bits.
The DS2148 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
(RUPCD1 and RUPCD2) registers and the Receive Down Code Definition (RDNCD1 and RDNCD2)
registers and the length of each pattern will be selected via the IBCC register. The DS2148 will detect
repeating pattern codes with bit error rates as high as 1x10
-2
. The code detector has a nominal integration
period of 48ms, hence, after about 48ms of receiving either code, the proper status bit (LUP at SR.7 and
LDN at SR.6) will be set to a one. Normally codes are sent for a period of 5 seconds. It is recommended
that the software poll the DS2148 every 100ms to 1000ms until 5 seconds has elapsed to ensure that the
code is continuously present.
IBCC (0AH): IN–BAND CODE CONTROL REGISTER
(MSB) (LSB)
TC1 TC0 RUP2 RUP1 RUP0 RDN2 RDN1 RDN0
SYMBOL POSITION DESCRIPTION
TC1 IBCC.7 Transmit Code Length Definition Bit 1. See Table 6-1
.
TC0 IBCC.6 Transmit Code Length Definition Bit 0. See Table 6-1
.
RUP2 IBCC.5 Receive Up Code Length Definition Bit 2. See Table 6-2
.
RUP1 IBCC.4 Receive Up Code Length Definition Bit 1. See Table 6-2.
RUP0 IBCC.3 Receive Up Code Length Definition Bit 0. See Table 6-2
.
RDN2 IBCC.2 Receive Down Code Length Definition Bit 2. See Table 6-2
.
RDN1 IBCC.1 Receive Down Code Length Definition Bit 1. See Table 6-2
.
RDN0 IBCC.0 Receive Down Code Length Definition Bit 0. See Table 6-2.