SN75LBC088

The SN75LBC088 attachment unit interface (AUI) concentrator chip (ACC) incorporates eight data terminal equipment (DTE) or station ports and one medium attachment unit (MAU) or global port on the same chip for connection to a local area network (LAN). Each station port emulates the driver/receiver functionality, timing, and signal response of a transceiver or MAU designed to meet the IEEE 802.3-1990 standard. The functional components of the ACC are a differential driver, collision detection driver, and a differential line receiver/squelch.

This device SN75LBC088 also has two operational modes, local and global, and a self-exerciser test mode. The SN75LBC088 uses the LinBiCMOSE process technology to ensure high-speed operation, analog precision, and low power consumption.

About SN75LBC088, Each of the eight station ports includes two differential drivers (STX1 thru STX8 [STXx] and SCL1 thru SCL8 [SCLx]) and one differential receiver [SRX1 thru SRX8 (SRXx)]. The SRXx (station receive) input pair is for receiving data sent from the station to the network. The STXx (station transmit) output pair is for transmitting network data to the station. The SCLx (station collision) output pair transmits the collision condition to the station.

The SN75LBC088 global port supports one differential driver (GTX) and two differential receivers (GRX and GCL). The GTX output pair drives data from a station port to the network. The GRX input pair receives network data from the external transceiver and channels it to all eight station ports. The GCL input pair receives network collision status to be forwarded to the individual station ports.

Each station port differential output pair of the SN75LBC088 drives a 78-W, balanced, terminated, twisted-pair transmission line up to 50 meters. In the off or idle state, the drivers maintain minimal differential output voltage on the twisted-pair lines and remain within the required output common-mode range. When the driver is internally enabled, the driver goes through what is called a soft start or half-step driver start up due to the first transition out of idle swings only half the normal differential amplitude. The differential outputs then rise to full amplitude output levels within 35 ns. The output amplitude is maintained for the remainder of the packet. After the last transmitted packet positive edge, the driver's enable circuit maintains the differential potential above the output common-mode voltage for at least 210 ns, decay down to a minimum differential voltage, and then return to an idle state. Each driver powers up in the idle state to ensure no activity is placed on the twisted-pair cable that could be interpreted as network traffic.

The line receiver squelch function interfaces to a differential twisted-pair line terminated external to the device SN75LBC088. The receiver squelch circuit allows differential receive signals to pass through while the input amplitude and pulse duration are greater than the minimum squelch threshold. This ensures a good signal-to-noise ratio while the data path is active and prevents system noise from causing false data transitions during line shut-down and line-idle conditions.

The SN75LBC088 functional control logic operates in two externally switched modes, local and global.Depending on the selected mode, the internal control logic selects the proper internal data path routing and collision handling. The internal data path is altered prior to enabling external line drivers to prevent data transmissions occurring during data path multiplexing.