Rainbow Electronics AT73C502 - Manual (Page 19)

AT73C500
19
Calibration
The calibration coefficients always have to be loaded into
AT73C500 registers after reset state. The coefficients are
either read from an external EEPROM or supplied by a
microprocessor via the 8-bit bus.
Loading of Calibration Coefficients
In modes 3 and 4, a microprocessor takes care that the
coefficients are kept in a non-volatile memory during volt-
age break. After the voltage break, the DSP first writes the
four header bytes, Sync LS, Sync MS, mode and status
information on the µP bus and then starts waiting for the
calibration data. The processor reads the status and mode
and after that writes the coefficients on the bus. The con-
tents of AT73C500 header bytes is described in “Data
Transfer to External Microprocessor” on page 12 and “Sta-
tus Information” on page 17.
Figure 14. Timing of calibration coefficient read operation
Before using the µP bus, AT73C500 writes a short pulse
(DATRDY) to B9 bit of the Status bus combined with high
level of address 0 (ADDR0 output). This bit can be taken
directly or through an external latch to the interrupt input of
the processor. After writing the status and mode bytes,
AT73C500 goes to a read mode and starts waiting for cali-
bration coefficients from the µP. Processor supplies the
coefficients as 8-bit bytes one after another. The timing of
this sequence is presented in Figure 14. Nine gain calibration, six offset calibration and three phase
calibration coefficients are read into the AT73C500 mem-
ory. At the same time, a scaling factor for the display pulse
rate and an adjustment value for starting current is stored.
To minimize the risk of erroneous calibration values, a
back-up value of each coefficient is also transferred by the
microprocessor or from the ROM. The back-up value has to
be written as 2’s complement binary number of the actual
calibration figure.
. . .
CLK
DATRDY
STROBE
HEADER DATA SUPPLIED BY AT73C500 44 COEFFEICIENTS READ
AT73C500 READY TO
READ CALIBRATION DATA
SYNC LS SYNC MS MODE STATUS COEFFICIENT 0
COEFFICIENT 1
COEFFICIENT 42
COEFFICIENT 43