MC68HC05V12 Datasheet, PDF (196/246 Pages) Freescale Semiconductor, Inc – HCMOS Microcontreller Unit

Gauge Drivers
Freescale Semiconductor, Inc.
For example, if the MIND1 register is written with any value, then the
MIND2 register must also be written. Otherwise, minor gauge D will not
be updated on subsequent scans and the currents driven into the coils
will maintain their previously programmed values. This sequence must
be followed even if the data written to one magnitude register is not
different from the data already in the register. The hardware works off
the write operation to the registers, not off the data written.
Before the master-to-slave transfer takes place in the CDRs, each coil in
a particular gauge must be updated. Because writes to the CMRs are the
only requirement for transferring master to slave of the CDRs, the CDRs
should be written before the CMRs are written.
15.7.1.2 Manual Mode
The user must set the SCNS bit in the scan status and control register
(SSCR) to initiate a scan cycle. Once a single scan cycle takes place,
the coil sequencer stops and waits for the SCNS bit to be set again
before starting another scan cycle. The SCNS bit must be set at a fast
enough rate (the scan period) to prevent the sample and hold circuits
from drooping and introducing error and current fluctuations into the
output currents. This minimum time is called the minimum scan period,
t_MSN (see 17.11 Gauge Driver Electricals). The transfer of data from
the CMR and CDRs master-to-slave buffers is performed at the
beginning of each gauge update time even if all CMRs and CDRs were
not updated.
If any of the gauges are turned off by clearing the appropriate bits in the
gauge enable register (GER), the time the coil sequencer would have
spent updating the coils in the disabled gauge is still expended, but the
coil driver remains off. This provides for a consistent scan rate
regardless of the number of gauges that are enabled.
The scanning sequence for the coils is shown in Table 15-1. It takes a
time, t_GCS, to update each coil. This includes time to move the data from
the CMR and CDR (automatic mode), perform the digital/analog
conversion, update the sample and hold circuit at the coil driver, and wait
for all transient currents to settle for each coil.
Technical Data
Gauge Drivers
For More Information On This Product,
Go to: www.freescale.com
MC68HC05V12 — Rev. 2.0