SN75LBC086

The SN75LBC086 is a single-channel differential driver/receiver interface device for the medium attachment unit (MAU) used in 10-MHz twisted-pair Ethernet applications. The device uses a 5-V supply and is designed to interface with two pairs of telephone-grade twisted-pair cables coupled through isolation transformers. The functional components of the device include a differential receiver and driver, receiver squelch with noise filter, jabber controls, collision detection, data link monitor, and signal quality error (SQE) testing. The LinBiCMOSE process technology is used in the device design to ensure analog precision, low power, and high-speed operation.

The device SN75LBC086 contains an elaborate receiver-squelch circuit† that provides an improved level of noise rejection by qualifying the incoming signal stream with three different criteria. First, the signal is compared to a set threshold voltage level. Then, the pulse duration is compared to a set time window. Last, the signal must follow a set pattern of positive and negative pulses before the circuit finally opens the receiver channel to the incoming data packet.

The SN75LBC086 jabber control is designed to prevent a defective controller from locking up the network by limiting the data packet transmission time to 20 to 30 ms. When a packet length exceeds 20 to 30 ms, the driver is turned off for about 600 ms. The driver-enable input must be made inactive by the controller during this period before the jabber control will release the driver. The JABB output is active (high) when a jabber condition exists.

Collision detection is used to arbitrate access to the multiuser network. This detection is done logically by monitoring the receive line for a valid signal during a driver transmission. When a collision is detected, this device SN75LBC086 informs the controller with an active-high CTL output. After a valid packet transmission, the device also performs a signal quality error test causing the CTL output to go active (high). This test is disabled when the SQEEN input goes inactive (high).

The device SN75LBC086 tests data-link integrity during the idle state by periodically driving the driver line with a unipolar pulse called a link-test pulse. The receiver looks for this link-test pulse on the receive line. A failed line link is indicated by a high-impedance state at the LINK output. This output drives an LED for monitoring if needed.

An internal test register is externally controlled with inputs FULLD and LOOP to select the device SN75LBC086 testing mode. When in the test mode, serial test-mode control patterns are clocked into the test register through input SQEEN. These control patterns select various modes to test the internal circuits.