Cromemco Inc.

Szu C Sun

Curtis G Terwilliger

Roger D Melen

W James McKeefery

An arbitrary number of member computer stations are inter-connected by a 'party' communication network. Each member station is normally in a high impedance Monitor Mode, for monitoring in-coming messages. The incoming messages latch the monitoring stations into a Receive Only Mode for preventing 'interrupts' of on-going communications. Each station continuously monitors the input impedance from the network, to determine when the network is available for transmission. Member stations may enter the low impedance Transmit Mode only when the network is available, because all of the other stations are in the Monitor Mode. A high Z from the network indicates to each station that the network is available. A low Z indicates that another station is in the transmit Mode, and is in control of the network. The random entry of two (or more) parties at the same time is resolved by a Pre-Transmission Test Cycle. Full transmit status with actual data transmission, cannot be obtained unless the Test code transmission reveals a high network impedance indicating that the network is available. In the 'two-party' start situation, each party senses the other parties low Transmit Mode impedance. Both parties drop back to the Monitor Mode, and a data 'collision' is avoided.

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Sunnyvale, CA, United States of America

Szu C Sun