DS1616

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General Communications Format

Communication with the DS1616 in both synchronous and asynchronous modes is accomplished by first

writing a command to the device. The command is then followed by the parameters and/or data required

by the command. The command set for the DS1616 can be seen in Table 3. Reads and writes to the

DS1616 differ in that writes are performed one byte at a time while reads are performed in page long (up

to 32-byte) bursts. Writing 1 byte at a time simply means that a write command has to be issued before

each byte of data that is written. For example, writing to the user NV RAM requires that the Write User

NV RAM command be written followed by the address to be written and then the actual data byte.

Writing a second data byte would require the same procedure with a new address specified. Reads,

however, are accomplished in bursts. For example, if an end user wants to read data from a specific page

he would first issue the Read Page command, followed by the address to begin reading. After the

DS1616 receives the command and starting address, it will immediately transmit the data that resides at

the given address location. However, rather than stop with that single byte of data, the DS1616 will

continue transmitting the next byte of data and will continue transmitting data until the page boundary is

reached. A page read can begin at any address, but will always end at the page boundary. Thus, a page

read can range from 1 to 32 bytes. It should be noted that a read can be terminated at any time when

DS1616 will not stop transmitting data until the page boundary is reached.

Cyclical Redundancy Check (CRC)

When communicating in the asynchronous mode, a 16-bit CRC is transmitted by the DS1616 following

the transmission of all data. When communicating in synchronous mode, no CRC is transmitted.

The 16-bit CRC (Cyclical Redundancy Check) is used to insure the accuracy of the data that is read from

the DS1616. The CRC is generated according to the standardized CRC16-polynomial function X16 +

X15 + X2 + 1. Figure 4 illustrates the function of the generator. The CRC is generated by clearing the

CRC generator and then shifting in data from the register set being read. A 16-bit CRC is transmitted by

the DS1616 after the last register of any page of memory is read. In other words, a CRC is generated at

the end boundary of every page that is read. The CRC is transmitted starting with bit 15 and ending with

bit 0.

CRC HARDWARE DESCRIPTION AND POLYNOMIAL Figure 4

BIT0

BIT1

BIT2

BIT3

BIT4

BIT5

BIT6

BIT7

BIT8

BIT9

XOR

XOR

XOR

BIT10

BIT11

BIT12

BIT13

BIT14

BIT15

CRC

OUTPUT

INPUT

DATA