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ST7285C Datasheet(HTML) 76 Page - STMicroelectronics

Part No. ST7285C
Description  8-BIT MCU FOR RDS WITH 48K ROM, 3K RAM, ADC, TWO TIMERS, TWO SPIs, I2C AND SCI INTERFACES
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Maker  STMICROELECTRONICS [STMicroelectronics]
Homepage  http://www.st.com
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ST7285C Datasheet(HTML) 76 Page - STMicroelectronics

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ST7285C
RDS G.B.S. (Cont’d)
GS_CNT - Count Register
b7-6 = CNB[1;0]
free-running 2-bit counter; used
as block/order counter. It is decremented on zero-
count of CNA[4:0]. The zero-counts of CNA and
CNB are used for counter interrupt generation. Re-
set Value equals one.
b5 = SYNC: Set to “1” whenever CNA[4;0] reach-
es a zero-count. it is valid for one period of
RDSCLK. Read only. SYNC flag is used when a
counter interrupt is desired on every RDSCLK
(used for general timing or ARI filter service), while
the BLK-SYNC interrupt service is performed eve-
ry 26 bits (CNA=26).
b4-0 = CNA[4:0]:
5-bit r/w autoreload counter;
used as RDS bit counter. It is decremented on
every rising edge of RDSCLK. When writing to
CNA, both a latch and the counter itself are writ-
ten. Immediately after reaching zero-count, the
contents of the latch are loaded back into the
counter (autoreload), so the zero-count state can
never be read by software. The zero-count of CNA
is used for counter interrupt generation. Reset Val-
ue equals one.
GS_INT - Interrupt Register
b7 = CAL:
Start Calculation. Writing a “1” into CAL
leads to a new syndrome calculation. CAL is al-
ways read as “0”. Used in software error correc-
tion.
b6 = CAR:
Calculation Running. Set to “1” by writ-
ing CAL=1. It returns to “0” when the syndrome
calculation is complete (VSI valid). Read only.
Used in software error correction.
b5 = ECM:
Error Correction Mode. If error correc-
tion by software is to be performed, ECM must be
set to “1”. This suppresses both shift and rotate
clocks for shift registers SR3-SR0, making them
available for software-triggered syndrome calcula-
tions which may require more than one RDSCLK
period. On completion of a correction, ECM must
be reset to “0” and the current status of SR3-SR0
must be retrieved from the shadow registers DR3-
DR0 by a copy routine.
b4 = VSI:
Valid Syndrome Interrupt. This flag is set
to “1” when the block code (BL[2:0]) is equal to one
of the six valid syndromes. Otherwise, it is reset to
“0”. VSI is valid on completion of a syndrome cal-
culation, for one period of RDSCLK. However, VSI
must be reset by software at the end of the inter-
rupt service routine. VSI and CNI interrupts are
ORed to the active-high level interrupt, ITSYNC.
b3 = VSE:
Valid Syndrome interrupt Enable. Set-
ting VSE to “1” enables the VSI interrupt.
b2 = CNI:
Counter Interrupt. This flag is set to
“1”on the zero-count of CNA/CNB or on the rising
edge of RDSCLK, depending on the setting of
CNE[1:0]. CNI is valid on completion of the syn-
drome calculation, for one period of RDSCLK.
However, CNI must be reset by software at the
end of the interrupt service routine. VSI and CNI
interrupts are ORed to the active high level inter-
rupt ITSYNC.
b1,0 = CNE[1:0]. Enables and selects the counter
interrupt, see Table 11 below:
Table 11. Counter Interrupt Source Selection
DR0 - RDSDAT Register 0
b7,6 = DR[1:0]. Receives RDSDAT sequence.
b5 = reserved, always read as “0”.
b4 = MQE:
Multiple Quality Error. Set to “1” when
2 or more low quality bit are detected during the
last block (26 bits). MQE is valid for one period of
RDSCLK, starting with CNA zero-count and is re-
set by hardware at the end of this period.
b3 = SQE:
Single Quality Error. Set to “1” when a
low quality bit is detected during the last block (26
bits). SQE is valid for one period of RDSCLK,
starting with CNA zero-count and is reset by hard-
ware at the end of this period.
b2 = QAL. Transparent QUALITY input signal
from RDS demodulator; read only.
b1 = RCL. Transparent RDSCLK input signal from
RDS demodulator; read only.
b0 = RDA. Transparent RDSDAT input signal from
RDS demodulator; read only.
DRx - RDS Data Registers
DR1. b7-0 contain bits 9-2 of a received RDSDAT
sequence.
DR2. b7-0 contain bits 17-10 of a received RDS-
DAT sequence.
DR3. b7-0 contain bits 18-25 of a received RDS-
DAT sequence.
CNE1
CNE0
Counter Interrupt Source Selection
0
0
counter interrupt disabled
01
counter interrupt on every rising edge
of RDSCLK
10
counter interrupt on CNA zero-count
state
11
counter interrupt on CNA & CNB zero
count states


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