System Considerations
MC1321x Reference Manual, Rev. 1.6
3-32
Freescale Semiconductor
(CCA), RX, and TX, and each has a separate current profile.
lists the typical currents while in
the listed modes, but does not show the transition profiles when moving between modes.
A normal sequence of events may include a 802.15.4 node performing first a CCA to see if the channel is
clear, second transmitting a frame (assuming the channel is clear), and finally after the TX, going into to
Receive Mode to look for an acknowledge. The modem must be programmed for each of the operations
separately and each operation has a different timing profile.
3.12.6.1.1
Modem CCA/ED Timing profile
The modem will scan for detected energy in a CCA operation (CCA is covered in detail in
“Clear Channel Assessment (CCA) Modes (including Link Quality Indication)”
). This is really a special
case of RX so the CCA current is the same as RX. There are two versions of CCA where one is called CCA
and the second is called Energy Detect (ED).
shows the timing profiles for both variations of a CCA operation. Once the CCA operation is
initiated, the state machine moves through a warm-up period of 144
μ
s in which the analog regulators turn
on and the analog RX circuitry comes to full power. The actual CCA or ED operation lasts 134
μ
s or 198
μ
s, respectively. During the warm-up period, the modem current is ramping from idle current (typically
500
μ
A) to full CCA current (typically 37 mA). The modem current for the CCA or ED is the full CCA
current. After the CCA/ED operation times out, the return to idle current is very quick.
Figure 3-10. CCA and ED Timing Profiles
Table 3-11. MC1321x Active State Currents
Mode
Current (typ @ 2.7V)
Idle
500
μ
A
CCA/ED
37 mA
RX
37 mA
TX
(0 dBm nominal
output power)
30 mA
Warmup
Idle
CCA
State:
Idle
Warmup
Idle
ED
State:
Idle
144
μ
s
134
μ
s
144
μ
s
198
μ
s
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