4.4.3.2.1.10 DMMB – Demodulator Mode for Path B

This register selects the main operating modes of the demodulator and the data filter. It must only be modified if the block receiving the settings is disabled (RDPR.PRPTA = 1). Modifying the settings during operation may lead to unstable operation.

Name:	DMMB
Offset:	0x0A1
Reset:	0x00


Bit	7	6	5	4	3	2	1	0
	DMNEB	DMHB	DMPB	DMATB[4:0]
Access	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset	0	0	0	0	0	0	0	0

Bit 7 – DMNEB Demodulator NRZ Enable for Path B

Table 4-23. DMNEB Bit Details
Bit 7	Description
`0`	Matched Manchester filter is used for data reception and TMDO output.
`1`	Symbol-based (NRZ) filter is used for data reception and TMDO output.

Bit 6 – DMHB Demodulator Hold Mode for Path B

Controls the operation of the DC compensation loop for the symbol-based data filter.

Table 4-24. DMHB Bit Details
Bit 6	Description
`0`	Hold mode deactivated – To be used for telegrams with up to two identical consecutive symbols. Adapts better to changing signal conditions. Not suitable for longer consecutive high or low periods.
`1`	Hold mode activated – To be used for NRZ or other reception with up to eight identical symbols in sequence. This mode freezes the DC compensation loop after a symbol change until the next signal edge is detected.

Bit 5 – DMPB Demodulator Received Data Polarity Selection for Path B

This register selects the data polarity at TMDO and RX buffer for path B. There is no effect on TRPB.

Table 4-25. DMPB Bit Details
Bit 5	Description
`0`	For Manchester coding: Rising edge in the middle of a bit is considered a ‘`1`’. For NRZ coding: Higher frequency (FSK) and active carrier (ASK) is considered a ‘`1`’.
`1`	For Manchester coding: Falling edge in the middle of a bit is considered a ‘`1`’. For NRZ coding: Lower frequency (FSK) and no carrier (ASK) is considered a ‘`1`’.

Bits 4:0 – DMATB[4:0] Demodulator Amplitude Threshold for Path B

Sets a minimum required modulation amplitude for the modulation amplitude check. An EOTS.AMPFB error is flagged if the selected modulation threshold is not exceeded by the incoming signal within two symbols (during WOK check if SY1TB is set) or within three symbols under all other circumstances. This check can also be used as an additional start of telegram condition (SOTSB.AMPOB). It is set to ‘1’ if no error occurred during the symbol check time. The recommended threshold is calculated differently for ASK and FSK modulation.

Recommended DMATB Setting for FSK

The maximum useful amplitude threshold for a given FSK signal depends on the expected deviation and the data rate settings:

D M A T A_M A X_F S K = r o u n d (\frac{M I N_D E V I A T I O N_B \times A T S C A L_B \times M A V F L_B \times 10}{C L K_B B \times P L L_G A I N_B}) (39)

Equation parameters:
- MIN_DEVIATION_B: The lowest possible frequency deviation in Hz of the useful signal on path B
- ATSCAL_B: Amplitude threshold scaling on path B. See DMDNB Setting versus Amplitude Threshold Scaling on Path B (ATSCAL_B) in the DMDRB from Related Links.
- MAVFL_B: Moving average filter length on path B. See DMAB Setting versus Moving Average Filter Length and Symbol Rate Factor on Path B (MAVFL_B, SR_F_B) in the DMDRB from Related Links.
- CLK_BB: Baseband clock frequency in Hz. See equation (13) in Bandwidth Scaling. See Bandwidth Scaling in the Channel Filter from Related Links.
- PLL_GAIN_B: FSK PLL gain on path B. See PLL Gain on Path B versus DMPGB Setting in the DMCRB from Related Links.
Using a higher value results in a very frequent or permanent error indication because the modulation amplitude threshold is similar to or higher than the minimum deviation (MIN_DEVIATION_B) of the useful signal.
The recommended setting for DMATB is half of the calculated maximum value (DMATB_MAX_FSK).
$D M A T B = r o u n d (\frac{D M A T B_M A X_F S K}{2}) (40)$
Raising this value increases the severity of this check.
Recommended DMATB Setting for ASK
$D M A T B = r o u n d (\frac{3 \times A T S C A L_B \times \sqrt{M A V F L_B}}{2^{\frac{D M D N B}{2}}}) (41)$
Equation parameters:
- ATSCAL_B: Amplitude threshold scaling on path B. See DMDNB Setting versus Amplitude Threshold Scaling on Path B (ATSCAL_B) in the DMDRB from Related Links.
- MAVFL_B: Moving average filter length on path B. See DMAB Setting versus Moving Average Filter Length and Symbol Rate Factor on Path B (MAVFL_B, SR_F_B) in the DMDRB from Related Links.
- DMDNB: Down-sampling on path B. See DMDNB Setting versus Amplitude Threshold Scaling on Path B (ATSCAL_B) in the DMDRB from Related Links.