DS1994L-F5 查看數據表（PDF） - Dallas Semiconductor -> Maxim Integrated
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DS1994L-F5 Datasheet PDF : 22 Pages
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Figure 3. 1-WIRE CRC CODE
Polynomial = X8 + X5 + X4 + 1
DS1994
1st
2nd
3rd
4th
STAGE STAGE STAGE STAGE
X0
X1
X2
X3
5th
STAGE
X4
6th
7th
8th
STAGE STAGE STAGE
X5
X6
X7
X8
INPUT DATA
MEMORY
The memory map in Figure 4 shows a 32-Byte page called the scratchpad, and additional 32-Byte pages
called memory. The DS1994 contains 16 pages that make up the 4096-bit SRAM. The DS1994 also
contains page 16, which has only 30 Bytes containing the timekeeping registers.
The scratchpad is an additional page that acts as a buffer when writing to memory. Data is first written to
the scratchpad where it can be read back. After the data has been verified, a copy scratchpad command
transfers the data to memory. This process ensures data integrity when modifying the memory.
TIMEKEEPING
A 32.768kHz crystal oscillator is used as the time base for the timekeeping functions. The oscillator can
be turned on or off by an enable bit in the control register. The oscillator must be on for the real-time
clock, interval timer, and cycle counter to function.
The timekeeping functions are double buffered. This feature allows the master to read time or count
without the data changing while it is being read. To accomplish this, a snapshot of the counter data is
transferred to holding registers that the user accesses. This occurs after the 8th bit of the read memory
function command.
Real-Time Clock
The real-time clock is a 5-Byte binary counter. It is incremented 256 times per second. The least
significant Byte is a count of fractional seconds. The upper 4 Bytes are a count of seconds. The real-time
clock can accumulate 136 years of seconds before rolling over. Time/date is represented by the number of
seconds since a reference point, which is determined by the user. For example, 12:00 A.M., January 1,
1970 could be a reference point.
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