Chapter 17 Voltage Regulator (S12VREG3V3V5)
MC9S12XDP512 Data Sheet, Rev. 2.11
Freescale Semiconductor 743
You can calculate the selected period depending of APICLK as:Period = 2*(APIR[11:0] + 1) * 0.1 ms or period = 2*(APIR[11:0] + 1) * bus clock period

Table 17-8. Selectable Autonomous Periodical Interrupt Periods

APICLK APIR[11:0] Selected Period
0 000 0.2 ms1
1When trimmed within specified accuracy. See electrical specifications for details.
0 001 0.4 ms1
0 002 0.6 ms1
0 003 0.8 ms1
0 004 1.0 ms1
0 005 1.2 ms1
0 ..... .....
0 FFD 818.8 ms1
0 FFE 819 ms1
0 FFF 819.2 ms1
1 000 2 * bus clock period
1 001 4 * bus clock period
1 002 6 * bus clock period
1 003 8 * bus clock period
1 004 10 * bus clock period
1 005 12 * bus clock period
1 ..... .....
1 FFD 8188 * bus clock period
1 FFE 8190 * bus clock period
1 FFF 8192 * bus clock period