COM20019IP datasheet(45/81 Pages) SMSC

45 / 81 page

DISCONTINUED DATASHEET

COMMAND CHAINING

The

Command

Chaining

operation

allows

consecutive transmissions and receptions to occur

without host microcontroller intervention.

Through the use of a dual two-level FIFO,

commands to be transmitted and received, as well

as the status bits, are pipelined.

In order for the COM20019 to be compatible with

previous SMSC ARCNET device drivers, the

device defaults to the non-chaining mode. In order

to take advantage of the Command Chaining

operation, the Command Chaining Mode must be

enabled via a logic "1" on bit 6 of the Configuration

In Command Chaining, the Status Register

appears as in Figure 9.

The following is a list of Command Chaining

guidelines for the software programmer. Further

detail can be found in the Transmit Command

Chaining

and

Receive

Command

Chaining

sections.

•

The device is designed such that the interrupt

service

routine

latency

does

not

affect

performance.

•

Up to two outstanding transmissions and two

outstanding receptions can be pending at any

given time. The commands may be given in

any order.

•

Up to two outstanding transmit interrupts and

two outstanding receive interrupts are stored

by the device, along with their respective

status bits.

•

The Interrupt Mask bits act on TTA (Rising

Transition

Transmitter

Available)

for

transmit

operations

and

TRI

(Rising

Transition of Receiver Inhibited) for receive

operations. TTA is set upon completion of a

packet transmission only. TRI is set upon

completion of a packet reception only.

Typically there is no need to mask the TTA

and TRI bits after clearing the interrupt.

•

The traditional TA and RI bits are still

available to reflect the present status of the

device.

Transmit Command Chaining

When the processor issues the first "Enable

Transmit to Page fnn" command, the COM20019

responds in the usual manner by resetting the TA

and TMA bits to prepare for the transmission from

the specified page. The TA bit can be used to see

if there is currently a transmission pending, but the

TA bit is really meant to be used in the non-

chaining mode only. The TTA bits provide the

relevant

information

for

the

device

the

Command Chaining mode.

COM20019IP датащи(PDF) 45 Page - SMSC Corporation

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