Rev. 1.0, 02/00, page 646 of 1141
26.8.5
Operation
The capstan speed error detector detects the speed error based on the reference value set in the
CFG specified speed preset register (CFPR). The reference value set in CFPR is preset in the
counter by the DVCFG signal, and the counter decrements the count by the selected clock. The
timing of the counter presetting and the error data latching can be selected between the rising or
falling edge of DVCFG signal. See DVCFG Control Register (CDVC) in section 26.14.3, CFG
Frequency Divider. The error data detected is sent to digital filter circuit. The error data is signed
binaries. The data takes a positive number (+) if the speed is slower than the specified speed, a
negative number (-) if the speed is faster, or 0 if it had no error (revolving at the specified speed).
Figure 26.33 shows an example of operation to detect the capstan speed.
Setting the Error Data Limit: A limit can be set to the error data sent to the digital filter circuit
using the CFG lock data register (CFRUDR, CFRLDR). Set the upper limit of the error data in
CFRUDR and the lower limit in CFRLDR, and write 1 in CFRFON bit. If the error data is outside
the limit range, the CFRLDR value is sent to the digital filter circuit if a negative number is
latched, or the CFRUDR value if a positive number is latched, as a limit value. Be sure to turn off
the limit setting (CFRFON = 0) when you set the limit value. If the limit was set with the limit
setting on (CFRFON = 1), result of computation is not assured.
Lock Detection: If an error data is detected within the lock range set in the lock data register, the
capstan lock flag (CF-R/UNR) is set by the number of the times of locking set by CFRCS1 and
CFRCS0 bits, and an interrupt is requested (IRRCAP2) at the same time. The number of the
occurrence of locking (once to 4 times) before the flag is set can be specified. Use CFRCS1 and
CFRCS0 bits for this purpose. The on/off state of the phase system digital filter computation can
be controlled automatically by the status of lock detection when bit 5 (CPHA bit) of the capstan
system digital filter control register (CFIC) is 0 (phased system digital filter computation off) and
DPCNT bit is 1.
Capstan System Speed Error Detection Counter: The capstan system speed error detection
counter stops the counter and sets the overflow flag (CFOVF) when an overflow occurs. At the
same time, it generates an interrupt request (IRRCAP1). To clear CFOVF, write 0 after reading 1.
If setting the flag and writing 0 take place simultaneously, the latter is invalid.
Interrupt Request: IRRCAP1 is generated by the DVCFG signal latch and the overflow of the
error detection counter. IRRCAP2 is generated by detection of lock (after the detection of the
specified number of times of locking).