Rainbow Electronics ATA5746 - Manual (Page 23)

23
4596A–RKE–05/06
ATA5745/ATA5746 [Preliminary]
6. Bit Rate Ranges
Configuration of the bit rate ranges is carried out via the two pins BR0 and BR1. The microcon-
troller uses these two interface lines to set the corner frequencies of the band-pass data filter.
Switching the bit rate ranges while the RF front end is in Active mode can be done on the fly and
will not take longer than 100 µs if done while remaining in either ASK or FSK mode. If the modu-
lation scheme is changed at the same time, the switching time is (T
Startup_Sig_Proc
, see Figure 7-1
on page 25 ). Each BR_Range is defined by a minimum edge-to-edge time. To maintain full sen-
sitivity of the receiver, edge-to-edge transition times of incoming data should not be less than the
minimum for the selected BR_Range.
Table 6-1. BR Ranges ASK
BR1 BR0 BR_Range
Recommended Bit Rate
(Manchester) (1)
Minimum Edge-to-edge
Time Period T
EE
of the Data
Signal (2)
Edge-to-edge Time Period T
EE
of
the Data Signal During the Start-up
Period (3)
0 0 BR_Range0 1.0 Kbit/s to 2.5 Kbits/s 200 µs 200 µs to 500 µs
0 1 BR_Range1 2.0 Kbits/s to 5.0 Kbits/s 100 µs 100 µs to 250 µs
1 0 BR_Range2 4.0 Kbits/s to 10.0 Kbits/s 50 µs 50 µs to 125 µs
1 1 BR_Range3 8.0 Kbits/s to 10.0 Kbits/s 50 µs 50 µs to 62.5 µs
Table 6-2. BR Ranges FSK
BR1 BR0 BR_Range
Recommended Bit Rate
(Manchester) (1)
Minimum Edge-to-edge
Time Period T
EE
of the Data
Signal (2)
Edge-to-edge Time Period T
EE
of
the Data Signal During the Start-up
Period (3)
0 0 BR_Range0 1.0 Kbit/s to 2.5 Kbits/s 200 µs 200 µs to 500 µs
0 1 BR_Range1 2.0 Kbits/s to 5.0 Kbits/s 100 µs 100 µs to 250 µs
1 0 BR_Range2 4.0 Kbits/s to 10.0 Kbits/s 50 µs 50 µs to 125 µs
1 1 BR_Range3 8.0 Kbits/s to 20.0 Kbits/s 25 µs 25 µs to 62.5 µs
Note: If during the start-up period (T
Startup_PLL
+ T
Startup_Sig_Proc
) there is no RF signal, the data filter settles to the noise floor, leading
to noise on pin DATA_OUT.
Notes: 1. As can be seen, a bit stream of, for example, 2.5 Kbits/s can be received in BR_Range0 and BR_Range1 (overlapping
BR_Ranges). To get the full sensitivity, always use the lowest possible BR_Range (here, BR_Range0). The advantage in
the next higher BR_Range (BR_Range1) is the shorter start-up period, meaning lower current consumption during Polling
mode. Thus, it is a decision between sensitivity and current consumption.
2. The receiver is also capable of receiving non-Manchester-modulated signals, such as PWM, PPM, VPWM, NRZ. In ASK
mode, the header and blanking periods occurring in Keeloq-like protocols (up to 52 ms) are supported.
3. To ensure an accurate settling of the data filter during the start-up period ( T
Startup_PLL
+ T
Startup_Sig_Proc
), the edge-to-edge
time T
EE
of the data signal (preamble) must be inside the given limits during this period.