DS1073
USER-PROGRAMMABLE REGISTERS
The following registers can be programmed by the user to determine operating frequency and mode of
operation. Details of how these registers are programmed can be found in a later section, in this section
the function of the registers are described. The register settings are non-volatile, the values being stored
automatically in EEPROM when the registers are programmed. Note: The register bits cannot be used to
make mode or frequency changes on the fly. Changes can only be made by powering the device up in
“Programming” mode. For them to be become effective the device must then be powered down and
powered up again in “Operation” mode.
For programming purposes the register bits are divided into two 9-bit words: the MUX word determines
mode of operation and prescaler values; the DIV word sets the value of the programmable divider.
MUX WORD Figure 2
(MSB)
(LSB)
E/ I
0*
0*
0*
PDN
M
DIV1
EN0
MSEL
*These bits must be set to 0
I
E/
This bit selects either the internal oscillator or the external/ crystal reference.
1 = External/Crystal
0 = Internal Oscillator
however, if the PDN bit is set to 0 the E/I bit will be overridden by the logic level on the PDN /SELX pin.
Table 1
( PDN / SELX
PDN
I
BIT
0
E/
PIN
OSCILLATOR MODE
X
0
EXTERNAL/CRYSTAL
0
X
X
0
1
INTERNAL
1
0
POWER-DOWN
INTERNAL
1
1
1
1
1
EXTERNAL/CRYSTAL
DIV1
This bit allows the master clock to be routed directly to the output (DIV1 = 1). The N programmable
divider is bypassed so the programmed value of N is ignored. The frequency of the output (fOUT) will be
INTCLK or EXTCLK depending on which reference has been selected. If the Internal clock is selected
the M prescaler may still be used, so in this case fOUT = INTOSC/M (which also equals MCLK and
INTCLK). If DIV1 = 0 the programmable divider functions normally.
MSEL
This bit determines whether or not the M prescaler is bypassed. MSEL = 1 will bypass the prescaler.
MSEL = 0 will switch in the prescaler, with a divide-by number determined by the M bit.
M
This bit sets the divide-by number for the prescaler. M = 0 results in divide-by-4, M = 1 results in divide-
by-2. The setting of this bit is irrelevant if MSEL = 1.
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DALLAS [ DALLAS SEMICONDUCTOR ]
