Rainbow Electronics ATA5757 - Manual (Page 6)

6
ATA5756/ATA5757 [Preliminary]
4702D–RKE–02/04
Transmission with
ENABLE = open
ASK Mode The ATA5756/ATA5757 is activated by ENABLE = open, FSK = High, ASK = Low. The
microcontroller is then switched to external clocking. After typically 0.6 ms, the CLK
driver is activated automatically (i.e., the microcontroller waits until the XTO and CLK
are ready). After another time period of
≤
250 µs, the PLL is locked and ready to transmit.
The output power can then be modulated by means of pin ASK. After transmission, ASK
is switched to Low and the microcontroller returns back to internal clocking. Then, the
ATA5756/ATA5757 is switched to power-down mode with FSK = Low.
Figure 4. Timing ASK Mode with ENABLE not Connected to the Microcontroller
FSK Mode The ATA5756/ATA5757 is activated by FSK = High, ASK = Low. The microcontroller is
then switched to external clocking. After typically 0.6 ms, the CLK driver is activated
automatically (i.e., the microcontroller waits until the XTO and CLK are ready. After
another time period of
≤ 250 µs, the PLL is locked and ready to transmit. The power
amplifier is switched on with ASK = H. The ATA5756/ATA5757 is then ready for FSK
modulation. The microcontroller starts to switch on and off the capacitor between the
crystal load capacitor and GND by means of pin FSK, thus, changing the reference fre-
quency of the PLL. IF FSK = L the output frequency is lower, if FSK = H output
frequency is higher. After transmission, FSK stays High and ASK is switched to Low and
the microcontroller returns back to internal clocking. Then, the ATA5756/ATA5757 is
switched to power-down mode with FSK = Low.
Figure 5. Timing FSK Mode with ENABLE not Connected to the Microcontroller
FSK
CLK
Power-up,
PA off
ASK
∆
T
XTO
Power-down
Power-up,
PA on
(High)
> 250 µs
Power-down
Power-up,
PA off
(Low)
FSK
CLK
Power-up,
PA off
ASK
∆
T
XTO
Power-down
Power-up,
PA on
(f
RF
= High)
> 250 µs
Power-down
Power-up,
PA off
(f
RF
= Low)