Rainbow Electronics ATA5757 - Manual (Page 7)

7
ATA5756/ATA5757 [Preliminary]
4702D–RKE–02/04
Transmission with
ENABLE = High
FSK Mode The ATA5756/ATA5757 is activated by ENABLE = High, FSK = High and 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 frequency of the PLL. IF FSK = L the output frequency is lower, if FSK = H
output frequency is higher. After transmission, ASK is switched to Low and the micro-
controller returns back to internal clocking. Then, the ATA5756/ATA5757 is switched to
power-down mode with ENABLE = Low and FSK = Low.
Figure 6. Timing FSK Mode with ENABLE Connected to the Microcontroller
ASK Mode The ATA5756/ATA5757 is activated by ENABLE = High, FSK = High and ASK = Low.
After activation the microcontroller is switched to external clocking. After typically
0.6 ms, the CLK driver is activated automatically (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 transmis-
sion, ASK is switched to Low and the microcontroller returns back to internal clocking.
Then, the ATA5756/ATA5757 is switched to power-down mode with ENABLE = Low and
FSK = 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)
ENABLE