COM90C66 datasheet(43/76 Pages) SMSC

43 / 76 page

NODE ID LOGIC

The Node ID code generated by the external

Node ID Select Switches is used to identify this

particular COM90C66. The code, which is input

by the COM90C66 in parallel format, is used by

the COM90C66 during transmission, reception,

reset, and reconfiguration.

Upon reset, the COM90C66 reads the Node ID

code set up on the switches and loads them into

the Node ID Register. For diagnostic purposes,

the Node ID may be read by the microprocessor.

The

ARCNET

protocol

maintains

that

destination Node ID of 00H will allow the source

node to broadcast a message.

In addition, in order to provide the user with

increased flexibility and to eliminate the cost of

the Node ID switch on board, the COM90C66

provides special circuitry which allows the user to

program the Node ID of any node via software.

To software program the Node ID register, the

Node ID switches of that node must be physically

set to 00H.

00H is not recognized by the

ARCNET protocol as a valid Node ID and

therefore is used only to switch to this special

mode. Setting the Node ID switches to all zero's

puts the COM90C66 into reset. The device will

not attempt to join the network and no microcode

is performed.

Tokens are not passed and

reconfigurations are not generated by the node.

The device will not attempt to rejoin the network

until a valid Node ID value is placed into the

Node ID Register.

For normal operation, the Node ID switches will

be set to some valid address between 01H and

FFH.

Writing a nonzero value to the Node ID

network.

TRANSMIT/RECEIVE LOGIC

Figure 13 illustrates the events which occur in

transmission or reception of data consisting of

1,1,0.

The COM90C66, during transmission,

produces two 100 nS nonoverlapping pulses on

the nPULSE1 and nPULSE2 lines to indicate a

logic "1", whereas a lack of pulses indicates a

logic "0". The nPULSE1 and nPULSE2 signals

are used to drive the HYC9058, the HYC9068 or

the HYC9088, which in turn creates a 200 nS

dipulse signal on the transmission media.

During reception, each dipulse appearing on the

transmission media is coupled through the RF

transformer of the LAN Driver to produce a

positive pulse on the RXIN pin.

The pulse is

captured

the

COM90C66

and

then

converted to NRZ data. Typically, RXIN pulses

occur at multiples of 400nS, plus or minus 100

nS and still correctly capture and convert the

RXIN pulses to NRZ format.

IMPROVED DIAGNOSTICS

The COM90C66 allows the user to better

manage the operation of the network through the

use of improved diagnostics within the device.

high

level

the

Reconfiguration

(MYRECON) bit indicates that the reconfiguration

which has just taken place was caused by this

particular

node.

After

the

Reconfiguration

(RECON) bit of the Status Register interrupts the

processor, the interrupt service routine will

typically

read

the

MYRECON

bit

the

Diagnostic

Status

Successive

occurrences of a logic "1" on the MYRECON bit

indicates that something is wrong with this node.

At that point, the transmitter should be disabled

so that the entire network is not continuously

brought down while the node is being evaluated.

The Receive Activity (RCVACT) bit of the

Diagnostic Status Register will be set to a logic

"1" whenever a rising edge of NRZ data is

detected on the RXIN pin.

The Token Seen (TOKEN) bit of the Diagnostic

Status Register will be set to a logic "1" whenever

any token has been seen on the network (except

COM90C66 Datasheet(PDF) 43 Page - SMSC Corporation

COM90C66 Datasheet(HTML) 43 Page - SMSC Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76

Datasheet Download

Link URL