
Extension Registers
14-51
`efmp69030 Databook
Revision 1.3 11/24/99
XRCC
Memory Clock VCO M-Divisor Register
read/write at I/O address 3D7h with index at I/O address 3D6h set to CCh
shared by both pipelines A and B
Note: All three of the registers used in specifying the loop parameters for the memory clock (XRCC -
XRCE) must be written, and in order from XRCC to XRCE, before the hardware will update the synthesizer’s
settings. This is a form of double-buffering that is intended to prevent fluctuations in the synthesizer’s output
as new values are being written to these registers.
7-0
Memory Clock VCO M-Divisor
These eight bits specify the M-divisor, one of the loop parameters used in controlling the
frequency of the output of the synthesizer used to generate the memory clock.
A series of calculations are used to derive this value and the values for the other loop
parameters given a desired output frequency and a series of constraints placed on different
components within the synthesizer used to generate the memory clock. See appendix B
for a detailed description of the process used to derive the loop parameter values.
XRCD
Memory Clock VCO N-Divisor Register
read/write at I/O address 3D7h with index at I/O address 3D6h set to CDh
shared by both pipelines A and B
Note: All three of the registers used in specifying the loop parameters for the memory clock (XRCC -
XRCE) must be written, and in order from XRCC to XRCE, before the hardware will update the synthesizer’s
settings. This is a form of double-buffering that is intended to prevent fluctuations in the synthesizer’s output
as new values are being written to these registers.
7-0
Memory Clock VCO N-Divisor
These eight bits specify the N-divisor, one of the loop parameters used in controlling the
frequency of the output of the synthesizer used to generate the memory clock.
A series of calculations are used to derive this value and the values for the other loop
parameters given a desired output frequency and a series of constraints placed on different
components within the synthesizer used to generate the memory clock. See appendix B
for a detailed description of the process used to derive the loop parameter values.
76543
210
A
&
B
Memory Clock VCO M-Divisor
76543
210
A
&
B
Memory Clock VCO N-Divisor