Electronic Components Datasheet Search |
|
AM79C98PC Datasheet(PDF) 9 Page - Advanced Micro Devices |
|
AM79C98PC Datasheet(HTML) 9 Page - Advanced Micro Devices |
9 / 22 page Am79C98 9 standard is generated at a transmitter and passed through 100 m of twisted-pair cable. The polarity detection/correction algorithm will remain “armed” until two consecutive packets with valid ETD of identical polarity are detected. When “armed,” the re- ceiver is capable of changing the initial or previous polarity configuration based on the most recent ETD polarity. On receipt of the first packet with valid ETD following reset or Link Fail, TPEX will utilize the inferred polarity information to configure its RXD ± input, regardless of its previous state. On receipt of a second packet with a valid ETD with correct polarity, the detection/correction algorithm will “lock in” the initial polarity. If the second (or subsequent) packet is not detected as confirming the previous polarity decision, the most recently de- tected ETD polarity will be used as the new default. Note that packets with invalid ETD have no effect on updating the previous polarity decision. Once two con- secutive packets with valid ETD have been received, TPEX will disable the detection/correction algorithm until either a Link Fail condition occurs or PRDN/RST is asserted. During polarity reversal, the RXPOL pin is internally pulled HIGH. During normal polarity conditions, the RXPOL pin is driven LOW and is capable of directly driving a “Polarity OK” LED using an integrated 16 mA driver. If desired, the polarity reversal function can be disabled by grounding the RXPOL pin. Twisted-Pair Interface Status Two outputs (XMT and RCV) indicate whether TPEX is transmitting (AUI to twisted-pair) or receiving (twisted- pair to AUI). Both signals are asserted during a colli- sion. In Link Fail mode, RCV is disabled. In Jabber Detect mode, XMT is disabled. Both signals are active HIGH. Collision Detect Function Simultaneous carrier sense (presence of valid data sig- nals) by both the AUI DO+/– pair and the RXD+/– pair constitutes a collision, thereby causing a 10 MHz signal to be asserted on the CI+/– output pair. The CI+/– output meets the drive requirements for the AUI. This 10 MHz signal will remain on the CI+/– pair until one of the two colliding states changes from active to idle. The CI+/– output pair stays HIGH for two bit times at the end of a collision, decreasing to the idle level within eighty bit times after the last LOW-to-HIGH transition. Both the XMT and RCV pins are driven HIGH during collision. Signal Quality Error (SQE) Test (Heartbeat) Function When the SQE TEST pin is driven LOW, TPEX will routinely exercise the collision detection circuitry by generating an SQE message at the end of every trans- mission. This signal is a self-test indication to the DTE that the MAU collision circuitry is functional. An SQE message consists of a 10 MHz signal on the CI+/– pair with a duration of 8 bit times (800 ns). When en- abled, an SQE Test will occur at the end of every trans- mission, starting eight bit times (800 ns) after the last transition of the transmitted signal. For repeater appli- cations, the SQE Test function can be disabled by tying the SQE TEST pin HIGH or by leaving it disconnected. Jabber Function The Jabber function inhibits the twisted-pair transmit function of TPEX if the DO+/– circuit is active longer than the time permitted to transmit the maximum- length 802.3/Ethernet data packet (50 ms nominal). This prevents any one node from disrupting the net- work due to a “stuck on” or faulty transmitter. If this maximum transmit time is exceeded, TPEX transmitter circuitry is disabled and a 10 MHz signal is driven onto the CI+/– pair. Once the transmit data stream is re- moved from the DO+/– pair of inputs, an “unjab” time of 250 ms to 750 ms will elapse before TPEX removes the 10 MHz signal from the CI+/– pair and re-enables the transmit path. Power Down In addition to on-board power-on-reset circuitry, the PRDN/RST pin is used as the master reset for TPEX. PRDN/RST must be driven LOW for a minimum of two microseconds for reset to occur. The PRDN/RST pin can also be used to put the TPEX into an inactive state, causing the device to consume less power. This feature is useful in battery-powered or low-duty-cycle systems. Driving PRDN/RST LOW resets the internal logic of TPEX and places the device into idle mode. In this mode, the twisted-pair driver pins (TXD+/–,TXP+/–) are driven LOW, the AUI pins (CI+/–, DI+/–) are driven HIGH, the LNKST and RXPOL pins are in the inactive state, and XMT and RCV are LOW. TPEX will remain in idle as long as PRDN/RST is asserted. Following the rising edge of the signal on PRDN/RST, TPEX will re- main in the reset state for 10 µs. Test Modes TPEX implements two types of loopback test modes suitable for Station (DTE) or Repeater applications. The Test mode is entered by driving the TEST pin HIGH. The two types of test modes available are: 1. Station (DTE): SQE TEST pin LOW. Data on DO+/– pair is transmitted onto the TXD+/– and TXP+/– pairs and data on the RXD+/– input pair is transmit- ted onto the DI+/– output pair. The jabber function and collision detection functions are disabled. 2. Repeater: SQE TEST pin HIGH. Data on DO+/– pair is looped back onto the DI+/– pair and data on the RXD+/– pair is retransmitted on the twisted-pair drivers (TXD+/– and TXP+/– pairs). |
Similar Part No. - AM79C98PC |
|
Similar Description - AM79C98PC |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |