Download

PDF Abstract Text:

High speed 8-bit parallel to serial converter

AN045

Philips Semiconductors Programmable Logic Devices
Application Note
High speed 8-bit parallel to serial converter
AN045
INTRODUCTION
A common function in many systems is to convert parallel data into a serial data stream. A microcontroller may be programmed to shift a byte in a register out to a port, but this is a relatively slow procedure. A simple pre-loadable shift register could perform the basic conversion. However, for the function to be complete, additional circuitry to perform handshaking or control of the process is required. The entire function can be made to fit into a low cost Programmable Logic Device (PLD), including control circuitry tailored to meet specific application requirements.
DESCRIPTION
Figure 1 shows the desired waveforms for a typical implementation. First, a reset signal initializes the system and this circuit. Next, the parallel data to be serialized is applied to the device, possibly from a parallel port of a microcontroller, and a write strobe (WRS) signal pulsed. The PLD then raises a flag (BUSY) and puts the data, one bit at a time, on an output (SDAT) under control of a clock signal (CLK). Another output, (SCLK) is an inverted copy of the transmitting clock, ANDed with a control signal, so it only is active when data is actually being sent. It can be used by the receiving device to clock in the serial data. How does one get a PLD to perform such a
RESET
ID7.ID0
SCLK SDAT
WRS CLK RESET
Figure 1. Desired Input and Output Waveforms
October 1993
Philips Semiconductors Programmable Logic Devices
Application Note
High speed 8-bit parallel to serial converter
AN045
COUNT
Figure 2. Waveform Timing Relationships
October 1993
Philips Semiconductors Programmable Logic Devices
Application Note
High speed 8-bit parallel to serial converter
AN045
October 1993
Philips Semiconductors Programmable Logic Devices
Application Note
High speed 8-bit parallel to serial converter
AN045
L 200 600
F1 : HELP, F10 : EXIT
October 1993