AN332
122
Confidential Rev. 0.2
Property 0x0201. REFCLK_FREQ
Sets the frequency of the REFCLK from the output of the prescaler. The REFCLK range is 31130 to 34406 Hz
(32768 ±5% Hz) in 1 Hz steps, or 0 (to disable AFC). For example, an RCLK of 13 MHz would require a prescaler
value of 400 to divide it to 32500 Hz REFCLK. The reference clock frequency property would then need to be set to
32500 Hz. RCLK frequencies between 31130 Hz and 40 MHz are supported, however, there are gaps in frequency
coverage for prescaler values ranging from 1 to 10, or frequencies up to 311300 Hz. The following table
summarizes these RCLK gaps:
Figure 3. REFCLK Prescaler
The RCLK must be valid 10 ns before sending and 20 ns after completing the AM_TUNE_FREQ and
AM_SEEK_START commands. In addition, the RCLK must be valid at all times for proper AFC operation. The
RCLK may be removed or reconfigured at other times. The CTS bit (and optional interrupt) is set when it is safe to
send the next command. This property may only be set or read when in powerup mode. The default is 32768 Hz.
Default: 0x8000 (32768)
Units: 1 Hz
Step: 1 Hz
Range: 31130–34406
Table 15. RCLK Gaps
Prescaler
RCLK Low (Hz)
RCLK High (Hz)
1
31130
34406
2
62260
68812
3
93390
103218
4
124520
137624
5
155650
172030
6
186780
206436
7
217910
240842
8
249040
275248
9
280170
309654
10
311300
344060
Bit
D15 D14 D13 D12 D11 D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
Name
REFCLKF[15:0]
Bit
Name
Function
15:0
REFCLKF[15:0]
Frequency of Reference Clock in Hz.
The allowed REFCLK frequency range is between 31130 and 34406 Hz (32768
±5%), or 0 (to disable AFC).
RCLK
REFCLK
PIN 9
Prescaler
Divide by
1-4095
31.130 kHz –
40 MHz
31.130 kHz –
34.406 kHz