November 6, 1997

ST-bus channel locator eases debugging

YS Tam, Canadian Marconi Co, Ottawa, ON, Canada

A simple circuit (Figure 1) can locate one of 32 channels in the serial stream of an ST-bus, which is helpful for both debugging and monitoring. The ST-bus comprises a framing signal for frame alignment, a clock signal for bit timing, and a serial information stream for data transmission. The clock rate is 2.048 Mbps, the frame signal is 8 kHz, and the serial information stream contains 32 channels with 8 bits per channel.

The setting of the 5-bit switch determines the selected channel. The chan_loc signal goes high to indicate the beginning of the selected channel and stays high for the whole period of the channel. The channel counter, chan_cnt in Listing 1, is always one channel ahead of the channel slot. Listing 1 is the VHDL source code for the EPM5032 (Altera Corp, San Jose, CA). Click here to download the file from DI-SIG, #2098. (DI #2098)

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