one-shot circuit output is directly applied to the lamp drivers. The lamp drivers cause the LSB lamp to come on amber and the USB lamp to come on green. Once the switchlight is released, an enter pulse is inserted into the word storage of the exhale word generator. If the IRC is in the manual mode, this enter pulse will cause the parallel transfer of the data bits from the one-shot circuits to the word storage register. When the switchlight is released, parallel data from the one-shot data is inhibited from the lamp drivers. The indicators change to the color configuration represented in the status configuration memory. The lamps go off momentarily because of the 25-millisecond cycle time of the roll call sequence required for updating the status registers. The parallel data goes from the word storage register to the parallel-to-serial word converter, and then, under control of the clock and roll call control, to the exhale word inhibit AND gate. From here it is transferred to the exhale word assembly register, where the roll call address and tag bit are added. A parity bit is also added if the first 35 bits are even. The clock pulse and data are combined and then shifted out on the multiplex line. The second part of the roll call 1 data is now in Manchester format and is applied to the other components on port 2. Only the SLU recognizes roll call 1 in its digital control section. Roll call 1 is an exhale word with respect to the IRC, but it is an inhale word in respect to the SLU. The inhale word enters the SLU through the line receiver and is transferred to the inhale word register. Here the data and the clock pulses are separated, and the data is shifted to the input register under the control of the derived clock pulses. This is the only function of the derived clock pulses. Once the data is shifted to the input register, the master clock is used to shift the data from one buffer to another. The roll call word is shifted into the valid word register. This register validates the word by ensuring that there are 36 bits, the address is 5 bits long, the address has a control list and a tag bit, and the word parity is odd. If any of these conditions are not met, the word is sent to the not-valid register. If the input word is invalid three times, the status register sets the BITE indicator on the component that sent the word. If the word is valid, a valid word signal is generated, and the enter bit of the derived data is examined. If the enter bit is not a binary one, no further processing is done. The SLU only processes data if a change is present on the inhale word. If a change is present, the enter bit is a binary one. If the inhale word is valid and it has an enter bit, it is sent to the HF configuration buffer. Here it is loaded into the multiplex register by the clock pulses and unique strobe G24. The multiplex input register shifts the data to the word decoder, where it is converted from serial binary format to parallel binary format. This parallel data is used to make the configuration change. The data is also converted back to serial binary format and stored for use in the exhale word assembly register for the next roll call 1. ROLL CALL 2.– After the second part of roll call 1 is processed by the SLU, the first part of roll call 2 is processed. Roll call 2 originates during word storage in the HF conjuration buffer of the SLU. The exhale word is sent from the SLU on the common multiplex line. Each component on the common multiplex line compares the address of roll call 2 with its own address. Only the IRC recognims roll call 2. The IRC processes the word in its digital control section the same way as the SLU did. The derived data is then sent to the input register where it is validated. The input register senses that the tag bit is a binary one. The binary one starts a 300-microsecond selective strobe counter and a 500-microsecond exhale word counter. The valid roll call 2 word is sent to all the display registers in the IRC, but because of the address, only the HF configuration status display register will receive clock pulses. The clock pulses will shift the roll call word into the inhale word decoder and storage register. Here it will wait until the selective strobe pulse transfers the parallel word to the lamp drivers. The selective strobe pulse is sent when the 300-microsecond counter times out, signaling the end of the inhale word time. The lamp drivers turn on the lamps by applying aground to the low side of the lamps. The high side of the lamps is supplied by the lamp dimmer control circuit. When the 500-microsecond timer times out, the IRC exhale word is applied to the multiplex lines. This word is the SLU inhale word, and it is processed exactly like the inhale word for roll call 1. The SLU will ensure that the enter bit is a binary one, and if so, will check the frequency to see if it is a legal frequency. If the frequency is legal, the word is processed and sent to the HF radio set in binary-coded-decimal (BCD) format. If the word is an illegal frequency, the frequency that is set upon the thumbwheel switches (on the SLU face) is sent to the HF set in BCD format. The operating frequency status word, which is the next word to be exhaled by the SLU, will equal the frequency that was sent to the HF radio set. If the frequency selected on the IRC is legal, 1-10