SMSC COM20020 manual Description of PIN Functions, A1,A2/ALE

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DESCRIPTION OF PIN FUNCTIONS

DIP PIN

PLCC PIN

NAME

 

 

 

NO.

NO.

SYMBOL

 

DESCRIPTION

 

 

 

 

 

 

 

MICROCONTROLLER INTERFACE

 

 

 

 

 

 

1-3

1-3

Address

A0/nMUX,

Input.

On a non-multiplexed bus, these

 

 

0-2

A1,A2/ALE

signals are directly connected to the low bits

 

 

 

 

of the host address bus. On a multiplexed

 

 

 

 

address/data bus, A0/nMUX is tied low, A1

 

 

 

 

is left open, and A2 is tied to the Address

 

 

 

 

Latch Enable signal of the host. A1 is

 

 

 

 

connected to an internal pull-up resistor.

 

 

 

 

 

4-11

4-6,8-12

Data 0-7

AD0-AD2,

Input/Output. On a non-multiplexed bus,

 

 

 

D3-D7

these signals are used as the data lines for

 

 

 

 

the device. On a multiplexed address/data

 

 

 

 

bus, AD0-AD2 act as the address lines

 

 

 

 

(latched by ALE) and as the low data lines

 

 

 

 

for the device. D3-D7 are always used for

 

 

 

 

data only. These signals are connected to

 

 

 

 

internal pull-up resistors.

 

 

 

 

 

 

23

27

nRead/nData

nRD/nDS

Input.

On a 68XX-like bus, this active low

 

 

nStrobe

 

signal is issued by the microcontroller as the

 

 

 

 

data strobe signal to strobe the data onto

 

 

 

 

the bus. On a 80XX-like bus, this active low

 

 

 

 

signal is issued by the microcontroller to

 

 

 

 

indicate a read operation. In this case, a

 

 

 

 

logic "0" on this pin, when the COM20020 is

 

 

 

 

accessed, enables data from the device to

 

 

 

 

the data bus to be read by the

 

 

 

 

microcontroller.

 

 

 

 

 

 

22

26

nWrite/

nWR/DIR

Input.

On a 68XX-like bus, this signal is

 

 

Direction

 

issued by the microcontroller as the

 

 

 

 

Read/nWrite signal to determine the

 

 

 

 

direction of data transfer. In this case, a

 

 

 

 

logic "1" selects a read operation, while a

 

 

 

 

logic "0" selects a write operation. In this

 

 

 

 

case, data is actually strobed by the nDS

 

 

 

 

signal. On an 80XX-like bus, this active low

 

 

 

 

signal is issued by the microcontroller to

 

 

 

 

indicate a write operation. In this case, a

 

 

 

 

logic "0" on this pin, when the COM20020 is

 

 

 

 

accessed, enables data from the data bus to

 

 

 

 

be written to the device.

 

 

 

 

 

 

4

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Contents Features General DescriptionTable of Contents PIN Configuration Description of PIN Functions A1,A2/ALETransmission Media Interface DIP PIN Plcc PIN Name Symbol DescriptionMiscellaneous Instead, it must be connected to XTAL1 with COM20020 Operation Network Reconfiguration Protocol DescriptionNetwork Protocol Data RatesBroadcast Messages Extended Timeout FunctionResponse Time Reconfiguration Time Idle TimeLine Protocol Invitations To TransmitAcknowledgements Data PacketsNegative Acknowledgements System Description MULTIPLEXED, 8051-LIKE BUS Interface with RS-485 Interface Figure C Backplane Configuration Traditional Hybrid InterfaceCOM20020 Network Using RS-485 Differential Transceivers Differential Driver Configuration Programmable Txen PolarityInternal Block Diagram Functional Description AttenuationNominal Cable Type Impedance AT 5MHZRead Register Summary Write Internal Registers Interrupt Mask Register IMRData Register Tentative ID RegisterDiagnostic Status Register Command RegisterNext ID Register Status RegisterConfiguration Register Setup Register BIT BIT Name Symbol Description BIT BIT Name Symbol Description DupidData Command Description Address Pointer High Register Address Pointer Low RegisterConfiguration Register ResetCKP3 CKP2 CKP1 Sequential Access Operation Sequential Access Memory Access SpeedInternal RAM Software InterfaceSelecting RAM Page Size Transmit SequenceRAM Buffer Packet Configuration Page Receive Sequence Command Chaining Transmit Command ChainingReceive Command Chaining Reset Details Internal Reset LogicImproved Diagnostics Initialization SequenceNormal Results Abnormal ResultsOscillator Maximum Guaranteed Ratings DC Electrical CharacteristicsParameter Symbol MIN TYP MAX Unit Comment Operational DescriptionXTAL1, XTAL2 Input Capacitance Timing Diagrams Multiplexed BUS, 68XX-LIKE Control Signals Read CycleMultiplexed 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 Normal Mode Transmit or Receive Timing These signals are to and from the hybridNTXEN NPULSE1 TTL Input Timing on XTAL1 PIN 28-PIN Plcc Package Dimensions 24-PIN DIP Package Dimensions Date SECTION/FIGURE/ENTRY Correction RevisedStandard Microsystems Corp