SMSC COM20020 manual DIP PIN Plcc PIN Name Symbol Description, Transmission Media Interface

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DIP PIN	PLCC PIN	NAME
NO.	NO.	NAME	SYMBOL	DESCRIPTION

19	23	nReset in	nRESET IN	Input. This active low signal issued by the
				microcontroller executes a hardware reset.
				It is used to activate the internal reset
				circuitry within the COM20020.

20	24	nInterrupt	nINTR	Output. This active low signal is generated
				by the COM20020 when an enabled
				interrupt condition occurs. nINTR returns to
				its inactive state when the interrupt status
				condition or the corresponding interrupt
				mask bit is reset.

21	25	nChip Select	nCS	Input. This active low signal issued by the
				microcontroller selects the COM20020 for
				an access.

TRANSMISSION MEDIA INTERFACE

16,15	19,18	nPulse 2,	nPULSE2,	Output.	In Normal Mode, these active low
		nPulse 1	nPULSE1	signals carry the transmit data information,
				encoded in pulse format, from the
				COM20020 to the media driver circuitry.
				When the device is in Backplane Mode, the
				nPULSE1 signal driver is programmable
				(push/pull or open-drain), while the
				nPULSE2 signal provides a clock with
				frequency of crystal/4.		nPULSE1 is
				connected to a weak internal pull-up resistor
				in backplane mode.

17	20	Receive In	RXIN	Input.	This signal carries the receive data
				information from the line receiver circuitry to
				the COM20020.

18	21	nTransmit	nTXEN	Output.	This signal is used prior to the
		nEnable		Power-upto enable the line drivers for
				transmission. The polarity of the signal is
				programmable by grounding the nPULSE2
				pin.
				nPULSE2 floating before Power-up: nTXEN
				active low (Default option)
				nPULSE2 grounded before Power-up:
				nTXEN active high (This option is only
				available in Backplane Mode)

			MISCELLANEOUS

13,14	16,17	Crystal	XTAL1,	An external crystal should be connected to
		Oscillator	XTAL2	these pins. If an external TTL clock is used

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Contents General Description FeaturesTable of Contents PIN Configuration A1,A2/ALE Description of PIN FunctionsMiscellaneous DIP PIN Plcc PIN Name Symbol DescriptionTransmission Media Interface Instead, it must be connected to XTAL1 with COM20020 Operation Protocol Description Network ReconfigurationNetwork Protocol Data RatesResponse Time Extended Timeout FunctionBroadcast Messages Idle Time Reconfiguration TimeLine Protocol Invitations To TransmitNegative Acknowledgements Data PacketsAcknowledgements System Description MULTIPLEXED, 8051-LIKE BUS Interface with RS-485 Interface Figure C Traditional Hybrid Interface Backplane ConfigurationCOM20020 Network Using RS-485 Differential Transceivers Programmable Txen Polarity Differential Driver ConfigurationInternal Block Diagram Attenuation Functional DescriptionNominal Cable Type Impedance AT 5MHZRead Register Summary Write Interrupt Mask Register IMR Internal RegistersData Register Tentative ID RegisterCommand Register Diagnostic Status RegisterNext ID Register Status RegisterConfiguration Register Setup Register BIT BIT Name Symbol Description Dupid BIT BIT Name Symbol DescriptionData Command Description Address Pointer Low Register Address Pointer High RegisterReset Configuration RegisterCKP3 CKP2 CKP1 Sequential Access Operation Access Speed Sequential Access MemoryInternal RAM Software InterfaceTransmit Sequence Selecting RAM Page SizeRAM Buffer Packet Configuration Page Receive Sequence Transmit Command Chaining Command ChainingReceive Command Chaining Internal Reset Logic Reset DetailsInitialization Sequence Improved DiagnosticsAbnormal Results Normal ResultsOscillator DC Electrical Characteristics Maximum Guaranteed RatingsParameter Symbol MIN TYP MAX Unit Comment Operational DescriptionXTAL1, XTAL2 Input Capacitance Multiplexed BUS, 68XX-LIKE Control Signals Read Cycle Timing DiagramsMultiplexed BUS, 80XX-LIKE Control Signals Read Cycle Multiplexed BUS, 68XX-LIKE Control Signals Write Cycle Multiplexed BUS, 80XX-LIKE Control Signals Write Cycle NON-MULTIPLEXED BUS, 80XX-LIKE Control Signals Read Cycle NON-MULTIPLEXED BUS, 68XX-LIKE Control Signals Read Cycle NON-MULTIPLEXED BUS, 80XX-LIKE Control Signals Write Cycle NON-MULTIPLEXED BUS, 68XX-LIKE Control Signals Write Cycle These signals are to and from the hybrid Normal Mode Transmit or Receive TimingNTXEN NPULSE1 TTL Input Timing on XTAL1 PIN 28-PIN Plcc Package Dimensions 24-PIN DIP Package Dimensions SECTION/FIGURE/ENTRY Correction Revised DateStandard Microsystems Corp