MC68HC05V12 Datasheet, PDF (200/246 Pages) Freescale Semiconductor, Inc – HCMOS Microcontreller Unit

Gauge Drivers
Freescale Semiconductor, Inc.
This bit clears automatically once the scan cycle begins to service coil
11 (minor D). The bit will clear at the proper time, even if the minor D
gauge is not enabled in the GER, since the scan cycle time is not
affected by the enabling or disabling of the gauges. The bit is cleared
once coil 11 begins to be serviced because adequate time (2 * t_GCS)
for the software (either interrupt driven or polled) to recognize the flag
and write new data to the CDR and CMR registers for the next scan
cycle should be provided. Note that after the scan cycle has finished,
a new scan cycle will not begin until this bit is set again. If a 1 is written
to this bit before it clears, the write will be ignored. In automatic mode,
this bit has no effect.
AUTOS — Automatic Mode Select Bit
This bit selects whether the coil sequencer will operate in manual or
automatic mode.
1 = Automatic mode
0 = Manual mode
15.8 Mechanism Diagram
The diagram in Figure 15-14 shows one way the gauge coils could be
connected to the coil driver pins and how some of the other pins should
be connected. The external components that have actual part numbers
are merely examples of suitable components. Other components with
similar operating characteristics also may be used.
15.9 Gauge Power Supply
The MC68HC705V12 contains most of the circuitry to provide the coil
drivers with a regulated supply that is necessary to drive the coil.
Referring to Figure 15-14, the gauge drive voltage, V_GSUP, is derived
with the aid of an external P-channel enhancement mode MOSFET
device which serves as the series pass devices between a +12 V supply
and the V_GSUP pin. Two external resistors also are used to set the level
of V_GSUP. The drive to the gate of the external pass devices will be
whatever is required to produce a V_GVREF voltage of 2.5. The value of
resistors R_G1 and R_G2 should be chosen so that
V_GSUP * [R_G2/(R_G1+R_G2)] = 2.5
Technical Data
Gauge Drivers
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MC68HC05V12 — Rev. 2.0