Freescale Semiconductor MC68HC908MR32 - Manual (Page 68)

Clock Generator Module (CGM)
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
68 Freescale Semiconductor
XLD — Crystal Loss Detect Bit
When the VCO output, CGMVCLK, is driving CGMOUT, this read/write bit can indicate whether the
crystal reference frequency is active or not. To check the status of the crystal reference, follow these
steps:
1. Write a logic 1 to XLD.
2. Wait N
× 4 cycles. (N is the VCO frequency multiplier.)
3. Read XLD.
The crystal loss detect function works only when the BCS bit is set, selecting CGMVCLK to drive
CGMOUT. When BCS is clear, XLD always reads as logic 0.
1 = Crystal reference is not active.
0 = Crystal reference is active.
PBWC[3:0] — Reserved for Test
These bits enable test functions not available in user mode. To ensure software portability from
development systems to user applications, software should write 0s to PBWC[3:0] whenever writing to
PBWC.
4.5.3 PLL Programming Register
The PLL programming register (PPG) contains the programming information for the modulo feedback
divider and the programming information for the hardware configuration of the VCO.
MUL[7:4] — Multiplier Select Bits
These read/write bits control the modulo feedback divider that selects the VCO frequency multiplier,
N. See
4.3.2.1 PLL Circuits and 4.3.2.4 Programming the PLL . A value of $0 in the multiplier select bits
configures the modulo feedback divider the same as a value of $1. Reset initializes these bits to $6 to
give a default multiply value of 6.
Address: $005E
Bit 7 6 5 4 3 2 1 Bit 0
Read:
MUL7 MUL6 MUL5 MUL4 VRS7 VRS6 VRS5 VRS4
Write:
Reset: 0 1 1 0 0 1 1 0
Figure 4-7. PLL Programming Register (PPG)
Table 4-2. VCO Frequency Multiplier (N) Selection
MUL7:MUL6:MUL5:MUL4 VCO Frequency Multiplier (N)
0000 1
0001 1
0010 2
0011 3
1101 13
1110 14
1111 15