3D7523

The 3D7523 is a monolithic CMOS Manchester Encoder/Decoder combo chip. The 3D7523 uses bi-phase-level encoding to embed a clock signal into a data stream for transmission across a communications link. In this encoding mode, a logic one is represented by a high-to-low transition in the center of the bit cell, while a logic zero is represented by a low-to-high transition.

The Manchester encoder combines the clock (CIN) and data (DIN) into a single bi-phase-level signal (TX). An inverted version of this signal (TXB) is also available. The data baud rate (in MBaud) is equal to the input clock frequency (in MHz). A replica of the clock input is also available (CBUF).

The encoder may be reset by setting the RESB input low; otherwise, it should be left high. The TX and TXB signals may be disabled (high-Z) by setting TXENB high. Similarly, CBUF may be disabled by setting CEN low. Under most operating conditions, TX and TXB are always enabled, and CBUF is not used. With this in mind, the 3D7523 provides internal pull-down resistors on CEN and TXENB, so that most users can leave these inputs uncommitted.

The Manchester decoder accepts the embedded-clock signal at the RX input. The recovered clock and data signals are presented on COUT and DOUTB, respectively, with the data signal inverted. The operating baud rate (in MBaud) is specified by the dash number of the device. The input baud rate may vary by as much as ±15% from the nominal device baud rate without compromising the integrity of the information received.

Because the decoder is not PLL-based, it does not require a long preamble in order to lock onto the received signal. Rather, the device requires at most one bit cell before the data presented at the output is valid. This is extremely useful in cases where the information arrives in bursts and the input is otherwise turned off.

Normally, the encoder and decoder function independently. However, if the LOOP input is set high, the encoded TX signal is fed back internally into the decoder and the RX input is ignored. This feature is useful for diagnostics. The LOOP input has an internal pull-down resistor and may be left uncommitted if this feature is not needed.