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MTD492 Datasheet(PDF) 5 Page - List of Unclassifed Manufacturers

Part No. MTD492
Description  Coaxial Transceiver Interface
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Maker  ETC [List of Unclassifed Manufacturers]

MTD492 Datasheet(HTML) 5 Page - List of Unclassifed Manufacturers

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MTD492 Revision 3.5 01/07/1997
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
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).
DC Supply Voltage(VEE)
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

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