MX828 查看數據表（PDF） - MX-COM Inc
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MX828 Datasheet PDF : 34 Pages
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CTCSS/DCS/SelCall Processor
21
MX828 PRELIMINARY INFORMATION
5.3 Receiver (CTCSS/SelCall Decoder)
The CTCSS/SelCall decoder should first be set up according to the desired characteristics. This entails setting the TONE
DECODER MODE Bit 2 of the SIGNALING SET UP Register ($82), and setting the TONE decoder bandwidth in the
SIGNALING SET-UP Register ($82), also programming the center frequencies of the desired tones in the RX TONE
PROGRAM Register ($84). (It can hold up to 15 different tones). Any tone can be in any location. When the device is
decoding, the tones are scanned in the sequence of their location, i.e. $0 first and $E last. Once a tone is detected the
remaining tones are not checked. Therefore if two tones are close enough in frequency for their bandwidths to overlap
then the one in the lowest location will be detected.
The TONE IRQ MASK in the IRQ MASK Register ($8E) should also be set as required.
The TONE DECODER ENABLE in the SIGNALING CONTROL Register ($80) should then be set to "1". While in the
CTCSS/SelCall decoder mode the fast/predictive detector may be enabled (see below). (Bit 5 in the SIGNALING
CONTROL Register $80).
When the CTCSS/SelCall decoder detects a change in its present state an IRQ will be generated and Bit 3 of the IRQ
FLAG Register ($8F) will indicate this.
The change that occurred can be read from Bit 4 of the SELCALL and SUB-AUDIO STATUS Register ($81) and if a tone
is indicated by this bit then the number of that tone can be read from Bits 3, 2, 1 and 0 of the same register.
5.4 Receiver (CTCSS Fast/Predictive Detector)
This is used for detecting, in the fastest possible time, that sub-audio tones are present on the Rx channel. Response time
is optimized for speed at the expense of frequency resolution.
It is enabled using Bit 5 of the SIGNALING CONTROL Register ($80). It has an IRQ which may be unmasked with Bit 2
of the IRQ MASK Register ($8E). The FAST CTCSS MODE DETECT/PREDICTIVE Bit 3 in the SIGNALING SET-UP
Register ($82) allows for one of two alternatives in the FAST mode. In DETECT mode it will detect any periodic tone in
the sub-audio band and when in PREDICTIVE mode it will detect specific tones determined by the frequency set in the
CTCSS TX/FAST RX FREQUENCY Register ($83) and the fixed PREDICTIVE mode bandwidth. Successful detection is
indicated by the CTCSS FAST IRQ FLAG Bit 2 in the IRQ FLAG Register ($8F), and the CTCSS FAST TONE Bit 6 in the
SELCALL and SUB-AUDIO STATUS Register ($81).
5.5 Receiver (DCS Decoder)
The incoming signal is matched with the DCS code programmed into the DCS BYTE 1/2/3 Registers. When the DCS
decoder is enabled, the DCS DECODE/NO DECODE FLAG in Bit 7 of the SELCALL and SUB-AUDIO STATUS Register
($81) will be set if the decode is successful (3 or fewer errors). A ''0" flag indicates a failure to decode. This flag is
updated for every bit of the incoming signal.
In order to detect the DCS turn-off code (134Hz) the CTCSS tone decoder should also be enabled and programmed with
this value. Once detected, this will cause a CTCSS tone decoder interrupt, the receiver audio output should then be
muted.
5.6 General Purpose Timer (GPT)
This may be used in conjunction with the CTCSS/SelCall decoder to form part of the decode algorithm or as a timer for
any other purpose. It has an 8-bit value in the GENERAL PURPOSE TIMER Register ($8B) set in units of 1msec, an IRQ
FLAG in Bit 6 of the IRQ FLAG Register ($8F) and an IRQ MASK in Bit 6 of the IRQ MASK Register ($8E).
5.7 Full Duplex Modes
Although the device is specified as half duplex, the only functions that must operate as such are:
DCS Tx
or DCS Rx
DCS Tx
or CTCSS Tx
CTCSS decode or SELCALL decode
All other functions are totally independent and therefore a full duplex CTCSS or full duplex SELCALL along with many
other combinations are possible.
© 1997 MX•COM Inc.
www.mxcom.com Tele: 800 638-5577 336 744-5050 Fax: 336 744-5054
Doc. # 20480161.002
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
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