Essel Technology RFID A1, User Manual, Page: 48 / 60

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4.2.24 Halt (0x18)
The Halt command takes no arguments. It halts the tag and turns off the RF field. It must be executed at the end of
each operation on a tag to disable the antenna and reduce the power consumption.
4.2.25 Calculate CRC (0x19)
Table 4.25
The Calculate CRC command takes as arguments the Memory Address, the Data Length in bytes and the Data Buffer
Offset. The CRC calculation starts at the byte pointed at by the memory address and is done on
the ‘ Data Length ’
number of bytes in the volatile memory. The result is stored in the Data Buffer at the Data Buffer Offset index. The
result is a 16-bit unsigned value with least significant byte first. The CRC calculation code is shown below.
static const uint16_t CCITTCRCTable [256] = {
0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5,
0x60c6, 0x70e7, 0x8108, 0x9129, 0xa14a, 0xb16b,
0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, 0x1231, 0x0210,
0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c,
0xf3ff, 0xe3de, 0x2462, 0x3443, 0x0420, 0x1401,
0x64e6, 0x74c7, 0x44a4, 0x5485, 0xa56a, 0xb54b,
0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6,
0x5695, 0x46b4, 0xb75b, 0xa77a, 0x9719, 0x8738,
0xf7df, 0xe7fe, 0xd79d, 0xc7bc, 0x48c4, 0x58e5,
Command Number
Command Name
Valid Tag Types
Argument Offset [bytes] 0x00 0x02 0x04
Argument Name Memory Address Data Length Data Buffer Offset
Argument Size [bytes] 0x02 0x02 0x01
Argument Description
Byte address in the
memory from which
the CRC calculation is
to start. This is an
unsigned 16-bit value
with least significant
byte first.
Data length in bytes
upon which the CRC is
to be performed. This
is an unsigned 16-bit
value with least
significant byte first.
Buffer offset in bytes
where the CRC value is
to be stored. The CRC
value is 16-bit
unsigned with least
significant byte first.
0x19
Calculate CRC
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