they can complete a full cycle. The decoding process is repeated, causing another derived clock pulse bit and another derive basic binary word bit to be generated. When a Manchester bit is a binary 0, it cannot reset the timers through the inverter. The 4.15-microsecond timer times out and produces a binary 1 at one input of the OR gate. The OR gate output is a binary 1 that represents the next derived clock pulse. Since there is a binary 1 at one input and a binary 0 at the other input of the AND gate, the resulting output is a binary 0 that represents the next derived data bit. The 8.3-micro- second timer is still running because a binary 1 has not been produced in the Manchester word. The 8.3-micro- second timer times out and produces a 1 on one input of the NAND gate. The other input is a 0, which produces a 1 at the output. This 1 produces a 1 at the output of the OR gate, which represents a 1 for the derived clock pulse. Multiplex Transmission Multiplex transmission data consists of 32 roll call words with a period of 800 microseconds for each word. The total period of time required for all the words is 25.6 milliseconds. Therefore, any one of the specific roll call periods occurs every 25.6 milliseconds. A roll call word consists of an inhale word and an exhale word, each being 400 microseconds long. Each inhale and exhale word consists of 48 clock intervals of 8.3 microseconds each. These clock intervals correspond to data bits. Of the 48 bits, 6 bits precede the 36-bit Manchester word and 6 bits follow the word. This means that there are 12 bits between the inhale word and the exhale word, which totals 79.6 microseconds. This period of time allows the component to prepare itself to receive or transmit data. The SLU controls the ICCG. The roll call for the communication systems is generated there. Between the SLU and the other components of the ICCG, the exhale word is a status word Between the GPDC and the SLU, the exhale word is also a status word. The inhale word between the SLU and the other components of the ICCG is a command word that tells the SLU to change configuration or frequency. The status is the configuration that the com- munication systems are in at any specific instant, and is indicated by the color of the switchlight (amber, green, red, or dark). A configuration change occurs whenever a switchlight is depressed. For example, changing HF USB to HF LSB is a configuration change. Each component in the ICCG has a digital control section that controls all data entering or leaving the component. The IRC and components that respond to the SLU are the only more than one roll call address. In contrast, the crew ICS panel only has to respond to one roll call address. Because of this, the crew ICS panels use comparators instead of input register decoders. The address logic is hardwired into the aircraft cable connectors for each crew ICS panel. This allows only one address to compare true at each station, which makes the crew ICS panels inter- changeable. Roll Call The ICCG logic flow and roll call sequence are described in the following text. ROLL CALL 0.– Roll call 0 is a spare on both the inhale and exhale words. When the 800 microseconds have elapsed, the roll call generator produces roll call 1. ROLL CALL 1.– The first part of roll call 1 is exhaled from the SLU. Roll call 1 informs the GPDC that a change in configuration or status has occurred since the last roll call 1. The GPDC buffer and/or multiplex lines (port 2) receives the exhale word from the SLU. There are three components of the ICCG hooked up to port 2. The IRC is the only ICCG com- ponent that recognizes roll call 1, and it processes the roll call through the digital control section, line receiver, and inhale word register. In the inhale word register, the Manchester word is decoded into the clock pulses and the data word. The roll call is matched against the address, and the decision is made whether or not to proceed with the processing. The other two components are processing the roll call 1 at the same time, but because the address will not match, only the IRC will continue processing. In the IRC, the derived data is sent to the input register under the control of the derived clock pulses. Word validation begins at this time. As part of the word validation process, the tag bit is examined. The tag bit of roll call 1 is a binary 1 that identifies the word as a status word from the SLU. A tag bit identification word in the IRC is sent to the inhale/exhale word gate. At the same time, the roll call 1 is sent to the exhale word inhibit gate that starts a 500-microsecond timer. When the timer times out, the exhale AND gate is enabled and the data word is shifted into the exhale word assembly register. The second part of roll call 1 is generated in the IRC. The data originates in the exhale word generator, and it represents the HF configuration. The configuration of the data bits in the exhale word register is shown in table 1-2. Data bits 15 and 16 are USB and LSB. When the USB/LSB switchlight is depressed to change from USB to LSB, a pulse is generated that sets the bit 16 one-shot circuit. As long as the switchlight is depressed, the 1-8