MC68HC05V12 Datasheet, PDF (182/246 Pages) Freescale Semiconductor, Inc – HCMOS Microcontreller Unit

Gauge Drivers
Freescale Semiconductor, Inc.
15.2 Introduction
The MC68HC705V12 contains on-chip circuitry to drive six cross coil air
core gauges. Four of the gauge drivers are 3-pin drivers intended for
180° gauges (minor gauges) and two of the drivers are full 4-pin
H-bridge drivers for 360° gauges (major gauges). The output drivers for
both major and minor gauges operate in a current drive mode. That is,
the current in the gauge coils is controlled rather than the voltage across
the coil. The maximum amount of current that can be driven into any coil
is set by the value of the resistance between the I_Max and V_SSA pins. The
current driven into each coil is set by writing a hex value to the current
magnitude registers and the direction of current is selected by setting or
clearing the appropriate bits in the current direction registers. The ratio
of the current used to set the gauge deflection angle is software
configured. No particular drive technique is implemented in hardware.
15.3 Gauge System Overview
The circuitry contained within the MC68HC705V12 provides a great deal
of flexibility for driving the coils. The user specifies coil currents rather
than degrees of deflection. This allows the software to drive the coil
currents in a variety of ways. The user must specify the magnitude of the
current as well as the direction it should flow for full H-bridge drivers. Half
H-bridge drivers require specification of a magnitude only. Eight full H-
bridge drivers and four half H-bridge drivers support two 360° and four
180° gauges.
Figure 15-6 is a block diagram of the gauge driver module within the
MC68HC705V12. Each of the blocks requiring more description is
described in the following subsections.
There are 20 coil driver pins on the MC68HC705V12. These are
grouped into two types. The pins whose names start with MAJ are full
H-bridge coil drivers. A or B in the pin name indicates major gauge A or
B. A 1 or 2 in the name refers to coil 1 or coil 2 within the same gauge.
It is important to keep coils within the same gauge connected to the
same A or B coil driver pins. The + or − in the pin name indicates the
direction of current flow according to this convention: The current
Technical Data
Gauge Drivers
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MC68HC05V12 — Rev. 2.0