Rainbow Electronics T5761 - Manual (Page 19)

19
T5760/T5761
4561B–RKE–10/02
Digital Noise
Suppression
After a data transmission, digital noise appears on the data output (see Figure 26). Pre-
venting that digital noise keeps the connected microcontroller busy. It can be
suppressed in two different ways.
Automatic Noise
Suppression If the bit Noise_Disable (Table 9) in the OPMODE register is set to 1 (default), the
receiver changes to bit-check mode at the end of a valid data stream. The digital noise
is suppressed and the level at Pin DATA is High in that case. The receiver changes
back to receiving mode, if the bit check was successful.
This way to suppress the noise is recommended if the data stream is Manchester or
Bi-phase coded and is active after power on.
Figure 28 illustrates the behavior of the data output at the end of a data stream. Note
that if the last period of the data stream is a high period (rising edge to falling edge), a
pulse occurs on Pin DATA. The length of the pulse depends on the selected baud-rate
range.
Figure 26. Output of Digital Noise at the End of the Data Stream
Figure 27. Automatic Noise Suppression
Figure 28. Occurrence of a Pulse at the End of the Data Stream
Data_out (DATA)
DATA_CLK
Preburst Data Digital Noise Preburst Data Digital Noise Digital Noise
Bit check ok
Bit-check
mode
Bit check ok
Receiving mode,
bit check aktive Receiving mode,
bit check aktive
Receiving mode,
data clock control
logic active Receiving mode,
data clock control
logic active
Data_out (DATA)
DATA_CLK
Preburst Data Preburst Data
Bit check ok Bit check ok
Bit-check
mode Bit-check
mode Bit-check
mode
Receiving mode,
data clock control
logic active Receiving mode,
data clock control
logic active
Dem_out
Data_out (DATA)
DATA_CLK
'1' '1' '1'
Timing error
T
ee
Bit-check mode Receiving mode,
data clock control
logic active
Data stream Digital noise
T Pulse
(t
ee
< T
Lim_min
OR T
Lim_max
< t
ee
< T
Lim_min_2T
OR t
ee
> T
Lim_max2T