- fc_div_2 <= fc_div_2 + 1;
-
-(* clock_signal = "yes" *) reg adc_clk;
-always @(xcorr_is_848, ck_1356megb, fc_div_2)
-if (xcorr_is_848)
- // The subcarrier frequency is fc/16; we will sample at fc, so that
- // means the subcarrier is 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 ...
- adc_clk <= ck_1356megb;
-else
- // The subcarrier frequency is fc/32; we will sample at fc/2, and
- // the subcarrier will look identical.
- adc_clk <= fc_div_2;
-
-
+ fc_div <= fc_div + 1;
+
+(* clock_signal = "yes" *) reg adc_clk; // sample frequency, always 16 * fc
+always @(ck_1356megb, xcorr_is_848, xcorr_quarter_freq, fc_div)
+ if (xcorr_is_848 & ~xcorr_quarter_freq) // fc = 847.5 kHz, standard ISO14443B
+ adc_clk <= ck_1356megb;
+ else if (~xcorr_is_848 & ~xcorr_quarter_freq) // fc = 423.75 kHz
+ adc_clk <= fc_div[0];
+ else if (xcorr_is_848 & xcorr_quarter_freq) // fc = 211.875 kHz
+ adc_clk <= fc_div[1];
+ else // fc = 105.9375 kHz
+ adc_clk <= fc_div[2];
+