HMC6352-EVAL Datasheet HMC6352-DEMO, HMC6352-EVAL, HMC6352-TR | P4-P6

HMC6352

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All bus transactions begin with the master device issuing the start sequence followed by the slave address byte. The

address byte contains the slave address; the upper 7 bits (bits7-1), and the Least Significant bit (LSb). The LSb of the

address byte designates if the operation is a read (LSb=1) or a write (LSb=0). At the 9

clock pulse, the recieving slave

device will issue the ACK (or NACK). Following these bus events, the master will send data bytes for a write operation, or

the slave will transmit back data for a read operation. All bus transactions are terminated with the master issuing a stop

sequence.

The following timing diagram shows an example of a master commanding a HMC6352 (slave) into sleep mode by sending

the “S” command. The bottom two traces show which device is pulling the SDA line low.

C bus control can be implemented with either hardware logic or in software. Typical hardware designs will release the

SDA and SCL lines as appropriate to allow the slave device to manipulate these lines. In a software implementation, care

must be taken to perform these tasks in code.

Command Protocol

The command protocol defines the content of the data (payload) bytes of I

C protocol sent by the master, and the slave

device (HMC6352).

After the master device sends the 7-bit slave address, the 1-bit Read/Write, and gets the 1-bit slave device acknowledge

bit returned; the next one to three sent data bytes are defined as the input command and argument bytes. To conserve

data traffic, all response data (Reads) will be context sensitive to the last command (Write) sent. All write commands shall

have the address byte least significant bit cleared (factory default 42(hex)). These commands then follow with the ASCII

command byte and command specific binary formatted argument bytes in the general form of:

(Command ASCII Byte) (Argument Binary MS Byte) (Argument Binary LS Byte)

The slave (HMC6352) shall provide the acknowledge bits between each data byte per the I

C protocol. Response byte

reads are done by sending the address byte (factory default 43(hex)) with the least significant bit set, and then clocking

back one or two response bytes, last command dependant. For example, an “A” command prompts the HMC6352 to

make a sensor measurement and to route all reads for a two byte compass heading or magnetometer data response.

Then all successive reads shall clock out two response bytes after sending the slave address byte. Table 1 shows the

HMC6352 command and response data flow.

0 1 0 0 0 0 1 0START

ACK

ACK STOP0 1 0 1 0 0 1 1

SDA

SCL

M_SDA

S_SDA

0 1 0 0 0 0 1 0START

ACK

ACK STOP0 1 0 1 0 0 1 10 1 0 0 0 0 1 0START

ACK

ACK STOP0 1 0 1 0 0 1 1

SDA

SCL

M_SDA

S_SDA

42(hex)

Write to This I

C Address

“S”

Command

HMC6352

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Table 1 – HMC6352 Interface Commands/Responses

Command

Byte

ASCII (hex)

Argument 1 Byte

(Binary)

Argument 2

Byte

(Binary)

Response 1

Byte

(Binary)

Response 2

Byte

(Binary)

Description

w (77)

EEPROM Address

Data

Write to EEPROM

r (72)

EEPROM Address

Data

Read from EEPROM

G (47)

RAM Address

Data

Write to RAM Register

g (67)

RAM Address

Data

Read from RAM Register

S (53)

Enter Sleep Mode (Sleep)

W (57)

Exit Sleep Mode (Wakeup)

O (4F)

Update Bridge Offsets (S/R Now)

C (43)

Enter User Calibration Mode

E (45

)

Exit User Calibration Mode

L (4C)

Save Op Mode to EEPROM

A (41) MSB Data LSB Data

Get Data. Compensate and

Calculate New Heading

Operational Controls

HMC6352 has two parameters; Operational Mode and Output Mode, which control its operation. The Operational Mode

control byte is located at RAM register byte 74(hex) and is shadowed in EEPROM location 08(hex). This byte can be used

to control the continuous measurement rate, set/reset function, and to command the HMC6352 into the three allowed

operating modes; Standby, Query, and Continuous.

The Output Mode control byte is located at RAM register byte 4E(hex) and is not shadowed in the EEPROM, and upon

power up the device is in the Heading output mode. This byte can be changed to get magnetometer data if necessary but

is typically left in a default heading data mode.

Non-Volatile Memory

The HMC6352 contains non-volatile memory capability in the form of EEPROM that retains key operational parameters

and settings for electronic compassing. Table 2 shows the balance of the EEPROM locations that the user can read and

write to. Details on the features of these location bytes will be discussed in the following paragraphs.

Table 2 – HMC6352 EEPROM Contents

EE Address (hex)

Byte Description

Factory

Default

C Slave Address

42(hex)

Magnetometer X Offset MSB

factory test value

Magnetometer X Offset LSB

factory test value

Magnetometer Y Offset MSB

factory test value

Magnetometer Y Offset LSB

factory test value

Time Delay (0

–

5 ms)

01(hex)

Number of Summed measurements(1

16)

04(hex)

Software Version Number

> 01(hex)

Operation Mode Byte

50(hex)

Operational Modes

The HMC6352 has three operational modes plus the ability to enter/exit the non-operational (sleep) mode by command.

Sleep mode sends the internal microprocessor into clock shutdown to save power, and can be brought back by the “W”

command (wake). The “S” command returns the processor to sleep mode. The three operational modes are defined by

two bits in the internal HMC6352 Operation Mode register. If the master device sends the “L” command, the current

operational mode control byte in the RAM register is loaded into the internal EEPROM register and becomes the default

operational mode on the next power-up. The application environment of the HMC6352 will dictate the most suitable

operational mode.

HMC6352

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Standby Mode: (Operational Mode=0) This is the factory default mode. The HMC6352 waits for master device

commands or change in operational mode. Receiving an “A” command (get data) will make the HMC6352 perform a

measurement of sensors (magnetometers), compute the compensated magnetometer and heading data, and wait for the

next read or command. No new measurements are done until another “A” command is sent. This mode is useful to get

data on demand or at random intervals as long as the application can withstand the time delay in getting the data.

Query Mode: (Operational Mode=1) In this mode the internal processor waits for “A” commands (get data), makes the

measurements and computations, and waits for the next read command to output the data. After each read command, the

HMC6352 automatically performs another get data routine and updates the data registers. This mode is designed to get

data on demand without repeating “A” commands, and with the master device controlling the timing and data throughput.

The tradeoff in this mode is the previous query latency for the advantage of an immediate read of data.

The above two modes are the most power conserving readout modes.

Continuous Mode: (Operational Mode=2) The HMC6352 performs continuous sensor measurements and data

computations at selectable rates of 1Hz, 5Hz, 10Hz, or 20Hz, and updates the output data bytes. Subsequent “A”

commands are un-necessary unless re-synchronization to the command is desired. Data reads automatically get the most

recent updates. This mode is useful for data demanding applications.

The continuous mode measurement rate is selected by two bits in the operational mode selection byte, along with the

mode selection and the periodic Set/Reset bit. The periodic Set/Reset function performs a re-alignment of the sensors

magnetic domains in case of sensor perming (magnetic upset event), operating temperature shifts, and normal thermal

agitation of the domains. Exposure of the HMC6352 to magnetic fields above 20 gauss (disturbing field threshold) leads to

possible measurement inaccuracy or “stuck” sensor readings until the set/reset function is performed. With the periodic

Set/Reset bit set, the set/reset function occurs every few minutes.

Operational Mode Control Byte Syntax

As described above, the HMC6352 operation mode, measurement rate, and periodic set/reset are selected and stored

both in a processor RAM register and in EEPROM. Upon power-up the EEPROM will transfer the saved operational mode

control byte into register address 74(hex). The following is the byte format:

Bit 7 =0

Bits 6 and 5 (Continuous Mode Measurement Rate)

Bit 6

Bit 5

Description

1 Hz Measurement Rate

5 Hz Measurem

ent Rate

10 Hz Measurement Rate

20 Hz Measurement Rate

Bit 4 (Periodic Set/Reset), 0 = Off, 1 = On

Bit 3 = 0

Bit 2 = 0

Bits 1 and 0 (Operational Mode Value)

Bit 1

Bit 0

Description

Standby Mode

Query Mode

Continuous Mode

Not Allowed

The total bit format for the Operational Mode Byte is shown below:

Bit 7 (MSB)

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0 (LSB)

M. Rate_H

M. Rate_L

Per. S/R

Op Mode_H

Op Mode_L

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