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PDF MTD492 Data sheet ( Hoja de datos )
| Número de pieza | MTD492 | |
| Descripción | Coaxial Transceiver Interface | |
| Fabricantes | Myson | |
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MYSON
TECHNOLOGY
MTD492
Coaxial Transceiver Interface
FEATURES
• Compatible with IEEE 802.3 10Base5 (Ethernet) and 10Base2 (Cheapernet).
• Internal AUI squelch circuitry for noise rejection.
• Transmission IDL detection at end of packet and dribble bit rejection window.
• Reception dribble bit rejection window.
• Reception and transmission mode collision detection.
• Extended collision detection to turn off receiving path.
• CD heartbeat externally controllable.
• Advanced low-power, high-performance CMOS technology.
• ESD protection greater than 2000 Volts.
• 16-pin PDIP and 28-pin PLCC packages.
GENERAL DESCRIPTION
The MTD492 transceiver integrates the coaxial cable interface functions of the Medium Attachment Unit
(MAU) in Ethernet or Cheapernet LAN applications. In an Ethernet 10Base5 network, MTD492 is mounted
on the thick Ethernet coaxial cable and connects to a station through an AUI cable. For Cheapernet
applications, MTD492 is connected to the Cheapernet coaxial cable through a BNC connector and is
usually mounted on the LAN adapter in a station.
BLOCK DIAGRAM
COAX
FXI
GND
125 XMT
10K
VEE
RECV
CDS
TXO
HIGH PASS
EQUALIZATION
LOW PASS
FILTER
LOW PASS
FILTER
COM
-
+
AUI
DRIVER
CARRIER
SENSE
AUI
DRIVER
RX+
RX-
CD+
CD-
TX+
LOW PASS
FILTER
- COLLISION
+
WAVEFORM
SHAPING
+
-
TX-
DC/AC
SQUELCH
10MHz CLK WATCH DOG
VEE
OSC
TIMER 26ms
RR+
1K
RR-
REFERENCE
CIRCUIT
TRANSMIT
STATE
MACHINE
HBE
JABBER RESET XMTSQ
TIMER 0.4sec
RECEIVE
STATE
MACHINE
This datasheet contains new product information. Myson Technology reserves the rights to modify the product specification without notice. No
liability is assumed as a result of the use of this product. No rights under any patent accompany the sale of the product.
MTD492 Revision 3.5 01/07/1997
1/8
1 page  
MYSON
TECHNOLOGY
MTD492
3.3. Collision Detection Path
In 10Base2 and 10Base5, a collision condition is determined by the DC level on the cable. The DC average
is extracted by a low pass filter. The output of the filter is compared with an internally set threshold (Vcd) to
determine the collision condition. The internal threshold is set for the reception-collision mode. By
definition, MTD492 will detect collision conditions caused by more than 2 stations simultaneously
transmitting.
The collision detection threshold can be shifted by applying a voltage to the CDS pin. This is typically done
by a resistor divider network between GND and VEE to implement the transmission-collision mode
detection. Transmission-collision differs from reception-collision in that transmission-collision will only
detect a 2-station collision if it is transmitting.
Once a collision is detected, MTD492 turns on the CD+/- pins. These 2 pins are also driven by source
followers, thus requiring external pull-down resistors. However, the followers are disabled during idle time,
and CD+/- will be pulled down to VEE and no current will flow through the external resistors.
Because Vcd is always larger than Vcs, when a collision occurs the reception path will also be turned on.
MTD492 implements an internal timer of 250 msec to detect the extended collision period. When a collision
condition period extends beyond this timer, the reception path is turned off. Any interruption of the collision
will reset the timer.
3.4. Reference and Control
The internal reference of MTD492 is generated by an on-chip bandgap circuit. An external resistor
connected between RR+ and RR- pins is used to set the reference current level. Typically, a precision 1K
Ohm resistor should be used. RR+ is internally shorted to GND, while RR- is biased at around -1.25V.
The heartbeat and jabber functions of MTD492 are implemented in the transmission state machine. The
heartbeat function is controlled by the HBE pin. MTD492 also provides a test mode that disables the jabber
function also controlled by the HBE pin. HBE has a 3-level input. It is biased internally at around -4.5V
(0.5Vee). When HBE is pulled high by a low value resistor (<4.7K), the heartbeat function is enabled; when
it is pulled low, the heartbeat is disabled. If it is driven to the mid-level or left floating, the jabber is disabled.
The exit of the jabber disable state takes about 0.5 sec (jabber reset time).
4.0 ABSOLUTE MAXIMUM RATINGS
DC Supply Voltage(VEE)
-12V
Input Voltage
GND+0.3 to VEE-0.3V
Storage Temperature
-65o to 150oC
Ambient Operating Temperature
0o to 70oC
ESD Protection except for Pin14
2000V
MTD492 Revision 3.5 01/07/1997
5/8
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet MTD492.PDF ] | |
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