Texas Instruments TCM4300 - Manual (Page 43)

4–8
Table 4–8. Typical Bit-Error-Rate Performance (WBD_BW = 000)
PARAMETER
TEST CONDITIONS
MIN MAX UNIT PARAMETER
MEAN CNR
MIN MAX UNIT
Bi
– 5 0.4
dB Bi
0 0.279
dB Bi
5 0.143
dB Bit error rate 10 0.056 dB
15 0.0192
20 0.00623
25 0.00199
The WBDD is controlled by the bits in the control register WBDCtrl (see Table 4–9).
Table 4–9. Bits in Control Register WBDCtrl
NAME BIT CODE FUNCTION
WBD_LCKD — Indicates whether edge detector is locked (1) or unlocked (0)
WBD_ON — Turns the WBDD module on/off (1/0)
WBD_BW Sets the appropriate PLL bandwidth
000 20 Hz
001 39 Hz
010 78 Hz
011 156 Hz
100 313 Hz
101 625 Hz
110 1250 Hz
WBD_LCKD: This bit reduces the effects of signal dropouts due to fading. In the Manchester-coded signal,
there are two types of data edges. One type occurs at the midpoint of each data bit, and the other occurs
randomly, depending on the transmitted data sequence. Inside the WBDD, an edge detector rapidly
synchronizes itself to the midpoint edges when the WBD_LCKD bit clears to 0. However, when a signal
dropout occurs, the edge detector may momentarily lock to the wrong edge because it cannot distinguish
the midpoint edges from the data edges. A small number of additional bits may be lost in this instance.
When the WBD_LCKD bit is set to 1, the edge detector uses the WBDD internal phase lock loop (PLL) output
to distinguish the correct edge. Once acquisition of data has occurred, when this bit is set to 1, the loss of
bits due to signal dropouts is restricted to the fade duration only.
When the WBDD PLL is not synchronized, as at power up, the WBD_LCKD bit must be cleared to 0 to allow
edge synchronization to the data.
WBD_BW: The variable bandwidth is required for fast acquisition in the beginning using a wide bandwidth
for the PLL, and a narrower bandwidth is used afterwards to reduce the likelihood of noise causing loss of
synchronization.
The WBDCtrl register is accessible by both the DSP and the microcontroller.
4.7 Wide-band Data Interrupts
The WBDD operates whenever WBD_ON is high, and it does not require the receive channels to be
enabled. While WBD_ON is high, every 800
µ
s, 8 bits are placed in the WBD register, which is accessible
by both the DSP and the microcontroller ports. This value should be written at the same time as WBD_ON
is initially set high.