MC68HC908GR8 Datasheet, PDF (84/286 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Clock Generator Module (CGMC)
7.5.5 PLL VCO Range Select Register
NOTE
PMRS may be called PVRS on other HC08 derivatives.
The PLL VCO range select register (PMRS) contains the programming information required for the
hardware configuration of the VCO.
Address:
Read:
Write:
Reset:
$003A
Bit 7
6
5
4
3
2
1
VRS7
VRS6
VRS5
VRS4
VRS3
VRS2
VRS1
0
1
0
0
0
0
0
Figure 7-8. PLL VCO Range Select Register (PMRS)
Bit 0
VRS0
0
VRS7–VRS0 — VCO Range Select Bits
These read/write bits control the hardware center-of-range linear multiplier L which, in conjunction with
E (see 7.3.3 PLL Circuits, 7.3.6 Programming the PLL, and 7.5.1 PLL Control Register), controls the
hardware center-of-range frequency, f_VRS. VRS7–VRS0 cannot be written when the PLLON bit in the
PCTL is set. (See 7.3.7 Special Programming Exceptions.) A value of $00 in the VCO range select
register disables the PLL and clears the BCS bit in the PLL control register (PCTL). (See 7.3.8 Base
Clock Selector Circuit and 7.3.7 Special Programming Exceptions.). Reset initializes the register to $40
for a default range multiply value of 64.
NOTE
The VCO range select bits have built-in protection such that they cannot be
written when the PLL is on (PLLON = 1) and such that the VCO clock
cannot be selected as the source of the base clock (BCS = 1) if the VCO
range select bits are all clear.
The PLL VCO range select register must be programmed correctly.
Incorrect programming can result in failure of the PLL to achieve lock.
7.5.6 PLL Reference Divider Select Register
NOTE
PMDS may be called PRDS on other HC08 derivatives.
The PLL reference divider select register (PMDS) contains the programming information for the modulo
reference divider.
Address:
Read:
Write:
Reset:
$003B
Bit 7
0
0
6
5
0
0
0
0
= Unimplemented
4
3
2
1
0
RDS3
RDS2
RDS1
0
0
0
0
Figure 7-9. PLL Reference Divider Select Register (PMDS)
Bit 0
RDS0
1
MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7
84
Freescale Semiconductor