u-blox M8 Series User Manual

000000 NEO-M8L - Hardware integration manual
UBX-16010549 - R08 Hardware description Page 8 of 28
C1-Public
☞ SPI is not available in the default configuration, because its pins are shared with the UART and
DDC interfaces. The SPI interface can be enabled by connecting D_SEL to ground. For speed and
clock frequency, see the corresponding product data sheet in the Related documents section.
1.4.5 TX Ready signal
The TX Ready signal indicates that the receiver has data to transmit. A listener can wait on the TX
Ready signal instead of polling the DDC or SPI interfaces. The UBX-CFG-PRT message lets you
configure the polarity and the number of bytes in the buffer before the TX Ready signal goes active.
The TX Ready signal can be mapped to UART TXD (PIO 06). The TX Ready function is disabled by
default.
☞ The TX Ready functionality can be enabled and configured by AT commands sent to the u-blox
cellular module supporting the feature. For more information, see the GPS Implementation and
Aiding Features in u-blox wireless modules [10].
1.5 I/O pins
1.5.1 RESET_N: Reset input
Driving RESET_N low activates a hardware reset of the system. Use this pin to reset the module only.
Do not use RESET_N to turn the module on and off, since the reset state increases power
consumption. With the NEO-M8L modules the RESET_N pin is an input only.
☞ Use RESET_N in critical situations only to recover the system. RESET_N also resets the real-time
clock which means that the receiver cannot perform hot start immediately after RESET_N.
1.5.2 WHEELTICK: Wheel tick input
The wheel tick input, also known as the HW interface, is used to provide speed pulse (wheel tick)
information to the NEO-M8L modules. By default the wheel tick count is based on the rising edge of
the wheel tick pulse signal. To improve performance with lower rate mechanically derived wheel-tick
signals, the receiver may be configured to use both the rising and falling edges of the wheel tick signal
on the condition that the wheel tick pulses have approximately 1:1 mark:space ratio regardless of
speed. The minimum recommended pulse width is 10 us.
The pulse interval (WT resolution) should be less than 40 cm per tick over distance travelled. For best
performance, less than 2 cm/tick is recommended. The wheel tick pulse output shall change linearly
with the change in speed (navigation filter estimates only the linear scale factor). If the vehicle is
standing still, there should be no wheel tick pulses. This is particularly important at system shut down
and power up. If there is a dead-band (wheel tick pulse does not change or is not output below a certain
speed), performance will be affected at low speed.
If the speed pulse is available from the host processor, then the information can also be provided by
SW interface using the UBX-ESF-MEAS message. In this particular case, the wheel-tick pin can be
configured as EXTINT1 and used to provide a time mark for the message. For more information, see
the u-blox 8 / u-blox M8 Receiver Description Including Protocol Specification [4].
☞ Do not exceed the maximum voltage of 3.6 V at the input when using the HW interface.
1.5.3 FWD: Forward/reverse input
The forward/reverse input is used to indicate the moving direction by an external signal (HW
interface). By default the wheel-tick direction pin polarity is automatically initialized once the vehicle
has reached required minimum speed of 30 km/h. The forward/reverse input polarity can also be set
manually. If the forward/reverse information is available from the host processor, the UBX-ESF-MEAS

u-blox M8 Series Specifications

General

Brand	u-blox
Model	M8 Series
Category	Control Unit
Language	English