SSC050-01 Datasheet, PDF (56/79 Pages) Maxim Integrated Products – Two-Wire Serial Backplane Controller

Control Registers
Control Register Definition
SSC050-01
Data Sheet
98h-9Bh: Pulse Width Modulation Control Registers (PWMC0-PWMC3)
Register Name:
Address:
Reset Value:
Description
PWMC0-PWMC3
98h-9Bh
X000_0000b
Pulse Width Modulation Control
These four registers provide a pulse width modulated output which can optionally be made available
on the P2.0 through P2.3 I/O pins. Configurations for these I/O pins which may have previously been
enabled through other control registers will be overridden if either or both of the PWBF bits are set.
The PWBF bits have higher priority control over the P2.0 through P2.3 I/O pins than any other mode
of operation. The pulse width modulated outputs are based on a 32 step counter and provide values
from a 3.125% to a 100% duty cycle in 3.125% increments.
7
6
5
4
3
2
1
0
Pulse Width Base Frequency
Pulse Width Percentage
Bit(s) Bit Label
6:5 PWBF1-0
Access Description
R/W Pulse Width Base Frequency
These two bits determine the base operating frequency of the pulse width modu-
lated output. These frequencies are based on the input clock rate of 10.0MHz. Three
additional base frequency ranges are available and are selected through bits 5 and 4
of the Backplane Controller Option Register located at address FDh. The following
table describes the default base frequencies:
4:0 PWP4-0
PWBF1
0
0
1
1
PWBF0
0
1
0
1
Pulse Width Base Frequency
normal operation - control is provided
through GPD1/DDP1 or BCP1
26KHz base frequency
52KHz base frequency
104KHz base frequency
R/W Pulse Width Percentage
These five bits determine the percentage of high time that the output pulse will con-
tain. There are 32 steps that can be adjusted in 3.125% increments. Table 4-9
describes the available percentages:
Table 4-9: Pulse Width Percentages
PWP4
0
0
0
PWP3
0
0
0
PWP2
0
0
0
PWP1
0
0
1
PWP0
0
1
0
Pulse Width Percentage
3.125% on/high time
6.25% on/high time
9.375% on/high time
Revision 4.0
November 10, 2004
4-40