HMR3100 SENSOR PRODUCTS HMR3100 Digital Compass Solution User’s Guide Solid State Electronics Center • www.magneticsensors.
HMR3100 SENSOR PRODUCTS INTRODUCTION The Honeywell HMR3100 is a low cost electronic compassing solution for use in consumer electronics and personal navigation products. Honeywell’s magnetoresistive sensors are utilized to provide enhanced reliability and accuracy in a small, two-axis, solid state compass design. This compass solution is easily integrated into systems using a simple UART interface and binary data format. Performance is optimized for a horizontal circuit board orientations.
HMR3100 SENSOR PRODUCTS converters (ADC) onboard a microcontroller (µC) integrated circuit. The microcontroller integrated circuit periodically samples the amplified sensor voltages, performs the offset corrections, and computes the heading. This microcontroller also performs the external serial data interface and other housekeeping functions such as the calibration routine.
HMR3100 SENSOR PRODUCTS USART Communication Protocol HMR3100 module communicates through binary data and ASCII characters at four selectable baud rates of 2400, 4800, 9600, or 19200. The default data bit format is USART 9600.N.8.1. The baud rate selection is determined by the position of jumpers J1 and J3. These jumpers are zero ohm SMT resistors (jumpers) and are normally high (logic 1) when removed, and grounded (logic 0) when in place. At 2400 baud, no jumpers are present for a 1,1 logic presentation.
HMR3100 SENSOR PRODUCTS Continuous Mode When the host processor (external to the HMR3100), holds the RTS input low, the HMR3100 will continuously send heading data via the TXD pin. The host shall hold the RXD pin high during this mode. The HMR3100 shall output the three-byte status/heading data packet at about a 2Hz rate. The HMR3100 will return to sleep mode when RTS is returned high. Figure 3 shows the continuous mode timing diagram.
HMR3100 SENSOR PRODUCTS Data Description The HMR3100’s onboard microcontroller sends a three byte status/heading data packet reply as the RTS line is brought low. The data is normally formatted in binary with the first byte being either 80(hex) or 81(hex). If that first byte LSbit is flagged high (81 hex), it means magnetic distortion maybe present and a hard-iron calibration should be performed. Many end users may choose to ignore this indication in portable applications.
HMR3100 SENSOR PRODUCTS Honeywell reserves the right to make changes to improve reliability, function or design. Honeywell does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others. 900284 02–04 Rev A Solid State Electronics Center • www.magneticsensors.
