DS2148T datasheet(40/75 Pages) DALLAS

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DS2148/Q48

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8. DIAGNOSTICS

8.1

In-Band Loop Code Generation and Detection

The DS2148 has the ability to 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 8-1

TC0

IBCC.6

Transmit Code Length Definition Bit 0. See Table 8-1

RUP2

IBCC.5

Receive Up Code Length Definition Bit 2. See Table 8-2

RUP1

IBCC.4

Receive Up Code Length Definition Bit 1. See Table 8-2

RUP0

IBCC.3

Receive Up Code Length Definition Bit 0. See Table 8-2

RDN2

IBCC.2

Receive Down Code Length Definition Bit 2. See Table 8-2

RDN1

IBCC.1

Receive Down Code Length Definition Bit 1. See Table 8-2

RDN0

IBCC.0

Receive Down Code Length Definition Bit 0. See Table 8-2

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