Ring/Carrier Detection And Interrupt - Epson S1C63558 Technical Manual

4.15.3 Ring/carrier detection and interrupt

The FSK block has a ring detection circuit and a carrier detection circuit built-in.
When a ring signal is input, the ring detection circuit sets the RDET bit (FF66H•D1) to "1" while the
signal is being input. In the same way, when a carrier is input, the carrier detection circuit sets the CDET
bit (FF66H•D0) to "1". Further, the interrupt can be generated at the rising edge or falling edge of these
detection signals. The edge selection can be made by the RDET comparison register RDETCP (FF67H•D1)
and CDET comparison register CDETCP (FF67H•D0).
When the register is set to "0", the interrupt is generated at the rising edge. When set to "1", the interrupt
is generated at the falling edge.
When the interrupt condition is met, the corresponding interrupt factor flag (the ring detection interrupt
= IRDET, the carrier detection interrupt = ICDET) is set to "1". In this case, when the corresponding
interrupt mask register (the ring detection interrupt = EIRDET, the carrier detection interrupt = EICDET)
has been set to "1", an interrupt request is generated to the CPU. When the interrupt mask register is set
to "0", the interrupt will be masked. However, even in this case, the interrupt factor flag is set to "1" when
the interrupt condition is met.
Figure 4.15.3.1 shows the relationship between the detection bit and the comparison register.
Comparison register
RDETCP CDETCP
0
With the above setting, the ring detection/carrier detection interrupt is generated under the following conditions:
By copying the RDET bit to the RDETCP register, the ring detection interrupt changes its generation timing
to the falling edge.
RDETCP CDETCP
1
Reset RDETCP and CDETCP in the initial status.
RDETCP CDETCP
0
By copying the CDET bit to the CDETCP register, the carrier detection interrupt changes its generation timing
to the falling edge.
RDETCP CDETCP
0
Fig. 4.15.3.1 Relationship between the detection bit and the comparison register
S1C63558 TECHNICAL MANUAL
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (FSK Demodulator)
0
RDET/CDET bit
(1) RDET CDET
0 0 (Initial value)
(2)
RDET CDET
1 0
0
(3)
RDET CDET
0 0
0
(4) RDET CDET
0 1
1
(5) RDET CDET
0 0
Ring detection interrupt generation
The interrupt is generated when the contents of RDET
are unmatched with the comparison register RDETCP.
Ring detection interrupt generation
The interrupt is generated at the falling edge.
Carrier interrupt generation
The interrupt is generated when the contents of CDET
are unmatched with the comparison register CDETCP.
Carrier detection interrupt generation
The interrupt is generated at the falling edge.
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