Abstract: Verification of test information transmitted across an 1149.1 backplane test bus between a circuit board (12.sub.1) and a test master (14) is accomplished by having both the test master and the circuit board compute a cheek code for each block of information that is transmitted by, or received at, the board. During intervals other than one of the active Boundary-Scan states, the test master (14) acquires the check codes produced at the circuit board (12.sub.1) and compares them to the corresponding codes generated by the tests master. Any difference between the corresponding codes generated by the test master and the circuit board signifies a transmission error.

Abstract: A plurality of individual systems (12.sub.o -12.sub.n) are controlled during testing via a test value present on a four-wire Boundary-Scan port (17). To accomplish such control, the test value present at the Boundary-Scan port is shifted through at least one buffer (16.sub.A) which generates a control signal on its output lines (S.sub.o -S.sub.7 ) in accordance with the test value. The control signal from the buffer controls at least one multiplexer (18.sub.A) and demultiplexer (18.sub.A') that collectively operate to select one of the systems in accordance with the buffer control signal.

Abstract: A method is provided for accomplishing unified testing of a digital/RF system (10'), comprised of a digital controller (14), a base-band processor (20), an RF transmitter (24) and an RF receiver (34). The digital portion of the digital/RF system (10'), including the digital controller (14) and the base-band processor (20), is tested by a digital test technique such as Boundary-Scan testing. Test patterns for the RF elements are down-loaded from the digital controller (14) to the base-band processor via a Boundary-Scan Test Access Port (TAP). Thereafter, the RF transmitter (24) and the RF receiver (34) are tested by applying the test patterns from the base-band processor to the RF transmitter for transmission thereby. The signal produced by the RF transmitter (24) in response to the applied test pattern is converted to a first digital signal stream for processing by the base-band processor (20) to determine the operability of the transmitter.