COM20051 datasheet(59/82 Pages) ETC1

59 / 82 page

Upon entering the ISR, the status register is read

and the TMA bit is checked. If the TMA bit is not

set, then the action as described above is taken.

If TMA is good then the interrupt is cleared and

either bit 6 or bit 5 of the TX_PEND_REG is

cleared

depending

the

number

transmissions

pending.

The

configuration

enable bit is checked. If Command Chaining is

enabled, then bit 4 of TX_PEND is set, otherwise

it is cleared.

A series of case statements are

then executed which read the TX_PEND_REG

and look for a set bit. If a bit is set in the lower

nibble, it signifies that the ARCNET RAM has

been loaded with data and that page is ready to

be transmitted.

Software should be written so

that an external routine will copy transmit data

into the ARCNET RAM. This will speed up the

ISR. Bits 5 and 6 are checked to see that the

pipeline is not completely filled. If they are both

set, then the routine is exited. If either one of the

bits

reset,

then

the

pending bit in TX_PEND_REG is reset, bit 5 or

6 is set, and an Enable to Transmit command is

given to the page corresponding to the bit

position in TX_PEND_REG.

Up to two transmit commands can be given

within the ISR at any given time.

If no

transmissions are pending, then the routine is

exited without any new transmissions.

Initiating Transmissions

The Transmit Service routine can only execute

after a transmission occurs.

Therefore, initial

transmit commands must originate from routines

external

the

Transmit

Interrupt

service

routine. The Transmit ISR can

only transmit

packets if and only if packets are pending

transmission

upon

entry

into

the

routine.

Normally

this

not

the

case,

thus

the

programmer must take care to monitor and

update

the

TX_PEND_REG

for

each

transmission.

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

TX_PEND_REG

RAM_BUF_REG

RX_PAGE_REG

NOT

USED

TX CMD #2

ISSUED

TX CMD #1

ISSUED

TX PEND.

BUFFER 4

NOT

USED

TX PEND.

BUFFER 3

TX PEND.

BUFFER 2

TX PEND.

BUFFER 1

NOT

USED

NOT

USED

NOT

USED

NOT

USED

NOT

USED

NOT

USED

RX BUF

RECEIVE COMMAND PAGE #2

RECEIVE COMMAND PAGE #1

COM20051 Datenblatt(PDF) 59 Page - List of Unclassifed Manufacturers

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