HMR3100 Honeywell International's Solid State Electronics Center (SSEC), HMR3100 Datasheet - Page 4

• Manufacturer Part Number: HMR3100
• Description: Digital Compass Solution
• Manufacturer: Honeywell International's Solid State Electronics Center (SSEC)

HMR3100
SENSOR PRODUCTS
The HMR3100 sends data via the TXD line (Pin 5) in standard serial bus form at logic levels, but uses the RTS (Pin
3) and RXD (Pin 6) to select the three active modes of operation. Normally RTS and RXD input lines are left high
until data or hard-iron calibration is needed from the HMR3100. The RXD line is left high unless a calibration is
requested. The RTS line will be either be pulsed low or held low to initiate an active mode. Otherwise a low-power
sleep mode is the default state. The RXD and RTS data inputs are passively pulled high via the microcontroller if left
open.
Normal Mode
When the host processor (external to the HMR3100), sends a RTS low pulse to the RTS pin, the HMR3100 will send
status/heading data via the TXD pin. The host shall hold the RXD pin high during this mode. The RTS shall be held
high when not pulsed. The HMR3100 will return to sleep mode when RTS is left high after the three-byte
status/heading data packet is sent. Up to 20 heading queries per second can be accomplished given fast enough
baud rates. A caution is advised that average current draw is proportional to supply voltage and amount of queries
handled. At the 20 Hz rate, 1 to 5 milliamperes of current is consumed with lesser query rates taking advantage of
the less than one-microampere sleep mode current draw between queries. Figure 2 shows the normal mode timing
diagram.
Figure 2
Normal Mode Timing Diagram
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.
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