Datasheet

Clock Generator Module (CGM)
MC68HC908GR60A • MC68HC908GR48A • MC68HC908GR32A Data Sheet, Rev. 5
84 Freescale Semiconductor
4.5.4 PLL Multiplier Select Register Low
The PLL multiplier select register low (PMSL) contains the programming information for the low byte of
the modulo feedback divider.
NOTE
For applications using 1–8 MHz reference frequencies this register must be
reprogrammed before enabling the PLL. The reset value of this register will
cause applications using 1–8 MHz reference frequencies to become
unstable if the PLL is enabled without programming an appropriate value.
The programmed value must not allow the VCO clock to exceed 32 MHz.
See 4.3.6 Programming the PLL for detailed instructions on choosing the
proper value for PMSL.
MUL7–MUL0 — Multiplier Select Bits
These read/write bits control the low byte of the modulo feedback divider that selects the VCO
frequency multiplier, N. (See 4.3.3 PLL Circuits and 4.3.6 Programming the PLL.) MUL7–MUL0 cannot
be written when the PLLON bit in the PCTL is set. A value of $0000 in the multiplier select registers
configures the modulo feedback divider the same as a value of $0001. Reset initializes the register to
$40 for a default multiply value of 64.
NOTE
The multiplier select bits have built-in protection such that they cannot be
written when the PLL is on (PLLON = 1).
4.5.5 PLL VCO Range Select Register
The PLL VCO range select register (PMRS) contains the programming information required for the
hardware configuration of the VCO.
NOTE
Verify that the value of the PMRS register is appropriate for the given
reference and VCO clock frequencies before enabling the PLL. See 4.3.6
Programming the PLL for detailed instructions on selecting the proper value
for these control bits.
Address: $0038
Bit 7654321Bit 0
Read:
MUL7 MUL6 MUL5 MUL4 MUL3 MUL2 MUL1 MUL0
Write:
Reset:01000000
Figure 4-7. PLL Multiplier Select Register Low (PMSL)
Address: $003A
Bit 7654321Bit 0
Read:
VRS7 VRS6 VRS5 VRS4 VRS3 VRS2 VRS1 VRS0
Write:
Reset:01000000
Figure 4-8. PLL VCO Range Select Register (PMRS)