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CHAPTER 3 FUNCTIONAL DESCRIPTION
User’s Manual S14054EJ4V0UM
31
(2) Non-back-to-back IPG
The non-back-to-back IPG set by the IPGR register is used to start outputting a transmit data stream to the PHY
device after transmission by another station has been completed and the IPG time has elapsed. The non-back-
to-back IPG consists of two portions. In the first half of the non-back-to-back IPG, carrier sense is performed. If
a carrier is detected during this time, the IPG count is cleared. The
µ
PD98431 waits until no carrier is detected
and starts IPG count again. If no carrier is detected during the period in which carrier sense is performed, the
µ
PD98431 immediately starts outputting a transmit data stream after the IPG period has elapsed.
The IPGR register sets the total time of the non-back-to-back IPG to the IPGR2 field, and the first half carrier
sense period to the IPGR1 field.
3.4.4 Collision and retransmission
The
µ
PD98431 automatically retransmits packets if a collision occurs, except if the number of collisions exceeds
the maximum number of times set by the CLRT register or if a collision occurs after the collision window period that is
also set by the CLRT register. If a collision occurs, data transmission from the transmit FIFO is stopped, and
transmission of jam is started. The read point in the transmit FIFO is returned to the beginning of the transmit data.
When transmission of a jam pattern has been completed, the
µ
PD98431 stands by for transmission in accordance
with the back-off algorithm. When the back-off period has expired, retransmission is automatically started.
If the number of collisions exceeds the maximum number of times set by the CLRT register or if it occurs after the
collision window period set by the CLRT register, it is regarded as a network error. If this happens, the data in the
transmit FIFO of the packet in which the condition occurs is cleared, and the other transmit packet data already
accumulated is not affected. The occurrence of this condition causes the INT# signal to go low. If the number of
collisions exceeds the maximum number of times, the ECOL bit of the TSVERG1 register is set to 1. If a collision
occurs after the collision window period, the LCOL bit of the TSVREG1 register is set to 1.
The interval of retransmission is determined by the back-off algorithm, and the
µ
PD98431 stands by for
retransmission for random slot time (512-bit time). This algorithm determines coefficient r of the slot time during
which the
µ
PD98431 stands by before executing the nth retransmission, by using the following expression:
0
≤
r < 2
n
, where n = 10 if n exceeds 10
3.4.5 End of or aborting transmission
The
µ
PD98431 ends or aborts transmission if any of the conditions described below is satisfied. If transmission is
aborted, the packet data remaining in the transmit FIFO is cleared. If transmission is aborted in the packet being
written to the transmit FIFO, all the data written to the transmit FIFO after transmission was aborted are ignored until
the end of data is specified by inputting the TXFDQ/FDQ signal (refer to
3.7.1 FIFO bus interface
).
Each time transmission has ended or has been aborted, the status information related to the transmission
operation is reported to the TSVREG1 and TSVREG2 registers. This status information can be used as an interrupt
source for the INT# signal by unmasking the interrupt by using the TIMR register.
(1) Normal completion
If data transmission is completed without problem, the TDONE bit of the TSVREG1 register is set to 1. If
retransmission due to collision takes place before transmission is completed, the number of times of
retransmission is reported to the TCBC field of the TSVREG1 register.
(2) Collision exceeding maximum number of times
If the number of collisions exceeds the maximum number of times set by the RETRY field of the CLRT register,
transmission is aborted and the ECOL bit of the TSVREG1 register is set to 1.
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