COM20019I-HT datasheet(29/65 Pages) SMSC

29 / 65 page

Low Cost ARCNET (ANSI 878.1) Controller with 2K x 8 On-Board RAM

SMSC COM20019I

Page 29

Rev. 03-07-06

DATASHEET

BIT

BIT NAME

SYMBOL

DESCRIPTION

Tentative ID

TENTID

This bit, if high, indicates that a response to a token whose DID

matches the value in the Tentative ID Register has occurred.

The second DID and the trailing zero's are not checked. Since

each node sees every token passed around the network, this

feature can be used with the device on-line in order to build and

update a network map. Refer to the Improved Diagnostics

section for further detail.

New Next ID

NEW

NXTID

This bit, if high, indicates that the Next ID Register has been

updated and that a node has either joined or left the network.

Reading the Diagnostic Status Register does not clear this bit.

This bit, when set, will cause an interrupt if the corresponding bit

in the IMR is also set. The bit is cleared by reading the Next ID

1,0

(Reserved)

These bits are undefined.

Table 6.5 - Command Register

DATA

COMMAND

DESCRIPTION

0000 0000

Clear

Transmit

Interrupt

This command is used only in the Command Chaining

operation. Please refer to the Command Chaining section for

definition of this command.

0000 0001

Disable

Transmitter

This command will cancel any pending transmit command

(transmission that has not yet started) and will set the TA

(Transmitter Available) status bit to logic "1" when the

COM20019I next receives the token.

0000 0010

Disable

Receiver

This command will cancel any pending receive command. If the

COM20019I is not yet receiving a packet, the RI (Receiver

Inhibited) bit will be set to logic "1" the next time the token is

received. If packet reception is already underway, reception will

run to its normal conclusion.

b0fn n100

Enable

Receive to

Page fnn

This command allows the COM20019I to receive data packets

into RAM buffer page fnn and resets the RI status bit to logic

"0". The values placed in the "nn" bits indicate the page that the

data will be received into (page 0, 1, 2, or 3). If the value of "f"

is a logic "1", an offset of 256 bytes will be added to that page

specified in "nn", allowing a finer resolution of the buffer. Refer

to the Selecting RAM Page Size section for further detail. If the

value of "b" is logic "1", the device will also receive broadcasts

(transmissions to ID zero). The RI status bit is set to logic "1"

upon successful reception of a message.

00fn n011

Enable

Transmit from

Page fnn

This command prepares the COM20019I to begin a transmit

sequence from RAM buffer page fnn the next time it receives

the token. The values of the "nn" bits indicate which page to

transmit from (0, 1, 2, or 3). If "f" is logic "1", an offset of 256

bytes is the start of the page specified in "nn", allowing a finer

resolution of the buffer. Refer to the Selecting RAM Page Size

section for further detail. When this command is loaded, the TA

and TMA bits are reset to logic "0". The TA bit is set to logic "1"

upon completion of the transmit sequence. The TMA bit will

have been set by this time if the device has received an ACK

from the destination node. The ACK is strictly hardware level,

sent by the receiving node before its microcontroller is even

aware of message reception. Refer to Figure 1 for details of the

transmit sequence and its relation to the TA and TMA status

bits.

COM20019I-HT Datasheet(PDF) 29 Page - SMSC Corporation

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