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Part: AM7996PC
Category:
Interface and Interconnect
Description: Ieee 802.3/ethernet/cheapernet Transceiver
Company: Advanced Micro Devices, Inc.
Datasheet: Download AM7996PC datasheet File size : 1108 kB
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FINAL
Am7996
IEEE 802.3/Ethernet/Cheapernet Transceiver
DISTINCTIVE CHARACTERISTICS
s Compatible with Ethernet Version 2 and IEEE 802.3 10BASE-5 and 10BASE-2 specifications s Pin-selectable SQE Test (heartbeat) option s Internal jabber controller prevents excessive transmission time s Noise rejection filter ensures that only valid data is transmitted onto the network s Collision detection on both transmit and receive data s Collision detect threshold levels adjustable for other networking applications
GENERAL DESCRIPTION
The Am7996 IEEE 802.3/Ethernet/Cheapernet Transc e i ve r suppor t s Ethernet Version 2, IEEE 802.3 10BASE-5 and IEEE 802.3 10BASE-2--Cheapernet) transceiver applications. Transmit, receive, and collision detect functions at the coaxial media interface to the data terminal equipment (DTE) are all performed by this single device. In an IEEE 802.3 (10BASE-5)/Ethernet application, the Am7996 interfaces the coaxial (0.4 diameter) media to the DTE through an isolating pulse transformer and the 78 attachment unit interface (AUI) cable. In IEEE 802.3 10BASE-2--Cheapernet applications, the Am7996 typically resides inside the DTE with its signals to the DTE isolated and the coaxial (0.2 diameter) media directly connected to the DTE. Transceiver power and ground in both applications are isolated from that of the DTE. The Am7996's tap driver provides controlled skew and current drive for data signaling onto the media. The jabber controller prevents the node from transmitting excessively. While transmitting, collisions on the media are detected if one or more additional stations are transmitting. The Am7996 features an optional SQE Test function that provides a signal on the Cl pair at the end of every transmission. The SQE Test indicates the operational status of the Cl pair to the DTE. It can also serve as an acknowledgment to the node that packet transmission onto the coax was completed.
BLOCK DIAGRAM
Carrier Detect Circuit DI+ DI Line Driver Control Logic Receive Data Amplifier Collision Detect Circuit Line Driver Control Logic Jabber Timer SQE Test Generator Input Buffer
RXT
Coaxial Media Interface
AUI Interface
CI+ CI
Transmit Squelch DO+ DO SQE TEST
Publication# 07506 Rev: E Amendment/0 Issue Date: May 1994
Input Buffer
Transmit Data Amplifier
Tap Driver
TXT
07506E-1
1
AMD
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CONNECTION DIAGRAMS
DIP
VCC1 CI+ CI DI+ DI VCREF SQE^TEST DO+ DO VEE 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 VCC2 COLL OSC VCOL NC RXT NC TAP SHIELD VTX TXT VTX+ DI+ DI VCREF SQE^TEST DO+ 4 5 6 7 8 CI+ VCC1 VCC2 CI
PLCC
COLL OSC VCOL NC RXT NC TAP SHIELD
3 2 1 20 19 18 17 16 15 14 9 10 11 12 13 DO VEE VTX+
TXT VTX
07506E-2
07506E-3
Notes: Pin 1 is marked for orientation. NC = No Connection
2
Am7996
ORDERING INFORMATION Standard Products
AMD standard products are available in several packages and operating ranges. The order number (valid combination) is formed by a combination of the elements below.
AM7996
D
C
B
OPTIONAL PROCESSING Blank = Standard Processing B = Burn-In TR = Tape and Reel Packaging
OPERATING CONDITIONS C = Commercial (0°C to +70°C)
PACKAGE TYPE P = 20-Pin Plastic DIP (PD 020) D = 20-Pin Ceramic DIP (CD 020) J = 20-Pin Plastic Leaded Chip Carrier (PL 020) SPEED Not Applicable DEVICE NUMBER/DESCRIPTION Am7996 IEEE 802.3/Ethernet/Cheapernet Transceiver
Valid Combinations AM7996 PC, PCB, DC, DCB, JC, JCTR
Valid Combinations Valid combinations list configurations planned to be suppor ted in volume for this device. Consult the local AMD sales office to confirm availability of specific valid combinations and to check on newly released combinations.
Am7996
3
PIN DESCRIPTION Attachment Unit Interface (AUI) Dl+, Dl
Receive Line Output (Differential Outputs) This pair is intended to operate into terminated 78 transmission lines. Signals at RXT meeting bandwidth requirements and carrier sense levels are outputted at D l ± . Signaling at Dl ± meets requirements of IEEE 802.3, Rev. D.
Global Signals VCREF
Timing Reference Set (Input) VCREF is a compensated voltage reference input with respect to VEE. When a resistor is connected between V CREF and V EE , then internal transmit and receive squelch timing, SQE oscillator frequency, and receive and SQE output drive levels are set. SQE frequency set is also determined by components connected between VCC1 and COLL OSC.
Cl+, Cl
Collision Line Output (Differential Outputs) This pair is intended to operate into terminated 78 transmission lines. Signal Quality Error (SQE), detected at DO ± inputs (excessive transmissions) or RXT input (during a collision), outputs the 10 MHz internal oscillator signal to the AUI interface. For proper component values at COLL OSC, signaling at Cl ± meets requirements of IEEE 802.3, Rev. D.
SQE TEST
Signal Quality Error Test Enable (Input) The SQE Test function is enabled by connecting the SQE TEST pin to VEE and disabled by connecting to VCC.
VTX+, VTX
Tap Node Driver Current Set (Inputs) A reference input for transmission level and external redundant jabber. Transmit level is set by an external resistor between VTX+ and VTX (for an 80 mA peak level, R = 9.09 ). VTX may be operated between VEE and VEE + 1 V. When the voltage at VTX goes more positive than VEE + 2 V, TXT is disabled and an SQE message is output at the Cl pair.
DO+, DO
Transmit Input (Differential Inputs) A pair of internally biased line receivers consisting of a squelch detect receiver with offset and noise filtering and a data receiver with zero offset for data signal processing. Signals meeting squelch requirements are waveshaped and output at TXT.
TAP SHIELD
Low-Noise Media Cable Return (Input) This input is the return for VCOL reference and the receive signal from the media. External connection is to a positive power supply.
Coaxial Media Interface (TAP) RXT
Media Signal Receiver Input (Input) RXT connects to the media through a 4:1 attenuator of 100 k total resistance (25 k and 75 k in series). Return for the attenuator is VCOL. RXT is an analog input with internal AC coupling for Manchester data signals and direct coupling for Carrier Detect and SQE average level detection. Signals at RXT meeting carrier squelch enable data to the Dl ± outputs. Data signals are AC coupled to Dl ± with a 150 ns time constant, high-pass filter. Signals meeting SQE levels enable COLL OSC frequency to Cl ± outputs.
VCOL
SQE Reference Voltage (Bias Supply) SQE sense voltage and RXT input amplifier reference. An internally set analog reference for SQE level and data signal set at 1.600 V nominal with a source resistance of 150 nominal. This reference should be filtered with respect to TAP SHIELD (see Applications section for adjusting threshold levels for other applications).
COLL OSC
SQE Timing Set (Input) Timing input for SQE oscillator. For a properly set input at VCREF, SQE oscillator period is set at 2.1RC. For a 10 MHz SQE oscillator frequency, R should be 1 k and C 47 pF, including interconnect and device capacitance.
TXT
Tap Node Driver (Input/Output) A controlled bandwidth current source and sense amplifier. This l/O port is to be connected to the media through an isolation network and a low-pass filter. Signals meeting DO ± squelch and jabber timing requirements are output at TXT as a controlled rise and fall time current pulse. When operated into a double termin a t e d 50 transmission line, signaling meets IEEE 802.3, Rev. D recommendations for amplitude, pulse-width distortion, rise and fall times, and harmonic content. The sense amplifier monitors TXT faults and inhibits transmission.
VCC1
Positive Logic Supply
VCC2
SQE Timing Reference (Positive Supply Voltage) Timing reference return for SQE oscillator and analog signal ground.
VEE
Negative Logic Supply and IC Substrate
4
Am7996
FUNCTIONAL DESCRIPTION
The Am7996 IEEE 802.3/Ethernet/Cheapernet Transceiver consists of four sections: 1) Transmit--receives signals from DTE and sends it to the coaxial medium; 2) Receive--obtains data from media and sends it to DTE; 3) Collision Detect--indicates to DTE any collision on the media; and 4) Jabber--guards medium from node transmissions that are excessive in length.
data to the differential line driver within five bit times from the start of the packet. Received data is transmitted from the Dl pair through an isolation transformer to the AUI cable (Ethernet/ lEEE 802.3--10BASE-5). In IEEE 802.3 10BASE-2-- Cheapernet, the AUI cable is optional. Following the last transition of the packet, the Dl pair is held HIGH for two bit times and then decreases to idle level within twenty bit times.
Transmit
The Am7996 receives differential signals from the DTE (in the case of Am7990 family applications, from the Am7992 --ser ial interface adapter--SIA). For IEEE (10BASE-5)/Ether net applications, this signal is received through the AUI cable and isolation transformer. In IEEE 802.3 10BASE-2--Cheapernet applications, the AUI cable is optional. Data is received through a noise rejection filter that rejects signals with pulse widths less than 7 ns (negative going), or with levels less than 175 mV peak. Only signals greater than 275 mV peak from the DTE are enabled. This minimizes false starts due to noise and ensures that no valid packets are missed. The Am7996's tap driver provides the driving capability to ensure adequate signal level at the end of the maximum length network segment (500 meters) under the worst-case number of connections (100 nodes). Required rise and fall times of data transmitted on the network are maintained by the Am7996 Tap Driver. The tap driver's output is connected to the media through external isolating diodes. To safeguard network integrity, the driver is disabled whenever power falls below the minimum operation voltage. During transmission, the Am7996 Jabber Controller monitors the duration that the transmit tap driver is active and disables the driver if the jabber time is exc e e d e d . This prevents network tie-up due to a "babbling" transceiver. Once disabled, the driver is not reset until 400 ms after the DO pair is idle and there is no fault on TXT. During the disable time, an SQE signal is sent on the Cl pair to the DTE. When SQE TEST is tied to VEE, the Am7996 generates an SQE message at the end of every transmission. This signal is a self-test indication to the DTE that the media attachment unit (MAU) collision pair is operational.
Collision Detect
The Am7996 detects collisions on transmit if one or more additional stations are transmitting on the network. Received signals are compared against the collision threshold reference. If the level is more negative than the reference, an enable signal is generated to the Cl p a i r. The collision threshold can be modified by external components. The collision oscillator is a 10 MHz oscillator that drives the differential Cl pair to the DTE through an isolation transformer. This signal is gated to the Cl pair whenever there is a collision, the SQE Test is in progress, or the jabber cont r o l l e r is activated. The oscillator is also utilized in counting time for the jabber timer and SQE Test. The Cl ± output meets the drive requirements for the AUI interface. The output stays HIGH for two bit times at the end of the packet, decreasing to the idle level within twenty bit times.
Jabber Function
The Am7996 Jabber Timer monitors the activity on the DO pair and senses TXT faults. It inhibits transmission if the tap driver is active for longer than the jabber time (26 ms). An SQE message (10 MHz collision signal), is enabled on the Cl pair for the fault duration. After the fault is removed, the jabber timer counts the unjab time of 400 ms before it enables the driver. If desired, a redundant jabber function can be implemented externally, and the output driver disabled by removing the driver supply at VTX.The Am7996 senses this condition and forces an SQE message on the Cl pair during the disable time.
SQE Test
An SQE Test will occur at the end of every transmission if the SQE TEST pin is tied to VEE. The SQE Test signal is a gated 10 MHz signal to the Cl pair. The SQE Test ensures that the twisted-pair assigned for collision notification to the DTE is intact and operational. The SQE Test starts eight bit times after the last transition of the transmitted signal and lasts for a duration of eight bit times. T h e SQE Test can be disabled by connecting the SQE TEST pin to VCC.
Receive and Carrier Detect
Signal is acquired from the tap through a highimpedance (100 k) resistive divider. A high inputi m p e d a n c e (low capacitance, high bandwidth, low noise) DC-coupled input amplifier in the Am7996 receives the signal. The received signal passes through a high-pass filter to minimize inter-symbol distortion, and then through a data slicer. The Am7996 Carrier D e t e c t compares received signals to a reference. Signals meeting carrier squelch requirements enable
Am7996
5
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