Circuit for Forming Test Message for Testing Serial Data Link
Original Publication Date: 1985-Aug-01
Included in the Prior Art Database: 2005-Feb-19
A microprocessor that has an 8-bit-wide data bus is used for testing a serial data link in which data is transmitted in frames of 16 bits. An improved test pattern is provided. In non-test operation, data is transferred from a parallel source to a 16-bit shift register and is serially shifted onto the serial link. For the test, the shift register is operated as two 8-bit registers. An 8-bit test pattern from the microprocessor is loaded simultaneously into each half register. The last stage of the left half register is connected to the first stage of the right half register by an inverter. The 8 bits loaded into the right register are shifted out normally and the 8 bits loaded into the left half register are shifted out inverted. Thus an 8-bit pattern is converted into a 16-bit test pattern frame.