RALCWI Vocoder
CMX608/CMX618/CMX638
6.
Application Notes
6.1.
Basic Operation of the Vocoder
This sequence of instructions assumes that the device is in its reset state and that the ENABXTAL pin is
set to '1'. The device may be reset, either by pulling the RESETN (pin 30) to '0' and then to '1', or by writing
to the RESET register ($01). The device will be ready to accept commands approximately 1.5 milliseconds
after a soft reset and will indicate that it is ready by setting bit 15 of the STATUS register ($40) to '1' and
also by indicating a C-BUS interrupt request (if enabled) by setting the IRQN pin to '0'.
The CMX608/CMX618/CMX638 device is for use in either an interrupt driven or a polled system. It will
indicate that it needs attention by setting a bit in the STATUS register and, if enabled, by taking the IRQN
pin to '0', thus generating an interrupt.
Initialisation:
1. Enable interrupts and establish internal processor speed
Write $C107 into the IRQENAB register ($1F)
Write $0005 into the CLOCK register ($1D)
Write $00 into the DTMFATTEN register ($0A).
Wait for a C-BUS interrupt or poll the STATUS register ($40) until bit 14 (SVC) is set to '1'.
For this example, all available interrupts have been enabled and the slow processor speed has
been selected with no DTMF attenuation.
2. Turn on BIAS and internal A/D and D/A converter (CMX618/CMX638 only)
Write $03 into the POWERSAVE register ($09).
Using the recommended 100nF bias capacitor: 100ms is required for the bias to reach its final
level.
3. Configure Vocoder
Write $37 into the VCFG register ($07).
This sets the Vocoder up to encode and decode 60ms packets of voice, using a Vocoder rate of
2400 bps data and 1200 bps FEC. Frames for decoding are expected to be hard bits.
4. Wait for configuration to complete
Wait for a C-BUS interrupt or poll the STATUS register ($40) until bit 15 is set.
Read the SVCACK register ($2E) and check that bit 0 is set to '1', which indicates that the device
has accepted the configuration. If this bit is not set to '1', it indicates that an incorrect value was
written to VCFG register.
The host should now wait for up to 100ms, to allow the bias capacitor to finish charging.
The device is now in a position to encode or decode. Step 5 or step 8 may now be executed.
Encoding:
5. Start encoder running (stop decoder if it was running)
Write $0002 into the VCTRL register ($11).
This tells the Vocoder to start collecting audio samples for encoding. If the device was previously
decoding, the decoder will be disabled and audio output will cease.
6. Wait for control command to complete
Wait for a C-BUS interrupt, or poll the STATUS register ($40) until bit 15 is set to '1'.
2012 CML Microsystems Plc
57
D/608_18_38/10
CMLMICRO [ CML MICROCIRCUITS ]
