TCM29C13A, TCM29C14A, TCM29C16A, TCM29C17A,

TCM129C13A, TC,129C14A, TCM129C16A, TCM129C17A

COMBINED SINGLE-CHIP PCM CODEC AND FILTER

SCTS030E – AUGUST 1989 – REVISED OCTOBER 1996

21

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

variable-data-rate timing

Variable-data-rate timing is selected by connecting DCLKR to the bit clock for the receive PCM highway rather

clocks FSX and FSR.

Variable-data-rate timing allows for a flexible data frequency. The frequency of the bit clocks can be varied from

64 kHz to 2.048 MHz. Master clocks in the TCM129C13A, TCM129C14A, TCM29C13A, and TCM29C14A are

restricted to frequencies of operation of 1.536 MHz, 1.544 MHz, or 2.048 MHz as in the fixed-data-rate timing

mode. The master clock for the TCM129C16A, TCM129C17A, TCM29C16A, and TCM29C17A is restricted to

2.048 MHz.

When the FSX/TSXE is high, PCM data is transmitted from PCM OUT onto the highway on the next eight

consecutive positive transitions of DCLKX. Similarly, while the FSR/TSRE input is high, the PCM word is

received from the highway by PCM IN on the next eight consecutive negative transitions of DCLKR.

The transmitted PCM word is repeated in all remaining time slots in the 125-

µs frame as long as DCLKX is pulsed

and FSX is held high. This feature, which allows the PCM word to be transmitted to the PCM highway more than

once per frame if desired, is available only with variable-data-rate timing. Signaling is allowed only in the

fixed-data-rate mode because the variable-data-rate mode provides no means with which to specify a signaling

frame.

signaling

Only the TCM29C14A provides 8th-bit signaling in the fixed-data-rate timing mode. Transmit and receive

signaling frames are independent of each other and are selected by a double-width frame-sync pulse on the

appropriate channel. During a transmit signaling frame, the signal present on SIGX is substituted for the least

significant bit (LSB) of the encoded PCM word. In a receive signaling frame, the codec decodes the seven most

significant bits in accordance with CCITT G.733 recommendations and outputs the logical state of the LSB on

SIGR until it is updated in the next signaling frame. Timing relationships for signaling operations are shown in

Figure 8. The signaling path is used to transmit digital signaling information such as ring control, rotary dial

pulses, and off-hook and disconnect supervision. The voice path is used to transmit prerecorded messages as

well as the call progress tones: dial tone, ring-back tone, busy tone, and reorder tone.