UPD360 datasheet(117/221 Pages) MICROCHIP

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 2016-2017 Microchip Technology Inc.

DS00002084C-page 117

UPD360

pending auto response GoodCRC request and another packet was received resulting in another auto response Good-

CRC request, the second request will replace the first request, unless the first request had a SOP type of SOP and the

second request had a SOP type of SOP'_Debug or SOP'’_Debug. This replacement occurs regardless of the setting of

the DIS_SOP_ABRTS_NON_SOP bit in the TX Control Register A (TX_CTL_A). Even if a received packet does not

abort a pending auto response, the pending auto response may get replaced by a new auto response.

11.1.5

AUTOMATIC RETRY MODE

The device also supports an Automatic Retry Mode. In this mode, when a GoodCRC message is not received in the

appropriate time (i.e., before CRCReceiveTimer expires) the current message is retried.

Hardware will retry the message until the retry value specified in the N_RETRY_CNT field in the TX Parameters Reg-

ister C (TX_PARAM_C) is satisfied. If the N_RETRY_CNT is set to zero, Automatic Retry Mode is disabled.

The number of retries used by the device to complete the transaction are tracked and made available to software via

the N_HW_RETRIES field in the TX Status Register (TX_STAT).

An N_RETRY_CNT value of zero implies the message is attempted only once, i.e., hardware will not retry it. N_RE-

TRY_CNT specifies the number of retries so the number of attempts is (N_RETRY_CNT + 1). Stated another way, if

you want hardware to make “N” attempts to send a message then the N_RETRY_CNT field must be set to “N-1.”

Reception of Hard Reset or Cable reset (when enabled and the SOP type of the pending TX is SOP', SOP'', SOP'_De-

bug or SOP''_Debug) from port partner, messages other than GoodCRC or Ping message (if the SOP types of the RX

and TX match or if the SOP type of the RX is SOP with the SOP type of TX being non-SOP (the latter can be disabled

via the DIS_SOP_ABRTS_NON_SOP bit in the TX Control Register A (TX_CTL_A)) and the packet was not a dupli-

cate), or issuance of abort by software will terminate any pending auto retries.

Detection of bus collision will cause the device to abort the current transfer including any pending auto retries unless

the RETRY_ON_LINE_BUSY bit in the TX Control Register A (TX_CTL_A) is set.

Note that disabling of automatic-retry by setting N_RETRY_CNT to zero will also disable the device’s ability to wait for

a GoodCRC message before a successful message transmission is indicated. This applies, for example, to the case

when Soft Reset is transmitted. To circumvent this limitation, a EXPECT_GOODCRC bit in the TX Parameters Register

A (TX_PARAM_A) is available. Setting this bit will cause the device to wait for a GoodCRC in response to a TX mes-

sage, even when the N_RETRY_CNT field is set to zero.

The expected message ID within the GoodCRC message is set by software via the MSG_ID field in the TX Parameters

The expected SOP type within the GoodCRC message is set by software via the TX_SOP_SELECT field in the TX

Parameters Register A (TX_PARAM_A). This is compared to the SOP type received in the GoodCRC message. In order

for the GoodCRC message to be received, it is assumed that the SOP type has been enabled via the RX_SOP_EN-

ABLE field in the RX Control Register B (RX_CTL_B).

11.1.6

IFG TIMER

The TX turn-around timer is used to insure that a minimum bus idle time is guaranteed between packet reception and

packet transmission, i.e., sending of GoodCRC message upon successful packet reception.

The value of this timer is programmable via the TX Turnaround Time Register (TX_TA_TIME). The value is specified in

uSec. This timer uses the free-running 1us pulse so the value of this register should be 1 more than desired to ensure

the minimum time.

11.1.7

CRC RECEIVE TIMER

This timer is enabled when the device is expected to wait for a GoodCRC ACK (i.e., automatic-retry mode is enabled

by non-zero value in the N_RETRY_CNT field of the TX Parameters Register C (TX_PARAM_C) or if zero, EXPECT_-

GOODCRC bit in the TX Parameters Register A (TX_PARAM_A) is set) at the time transmission is requested. This timer

can also be enabled for software usage via the EN_CRC_RCV_TMR bit in the RX Control Register A (RX_CTL_A).

If enabled, the timer starts whenever a TX packet transmission stops.

If software aborts a TX packet in between transmission with auto-retry mode enabled, this timer will not be triggered and

will be disabled. If software aborts a TX packet with auto-retry disabled, then it should also disable the timer by clearing

the EN_CRC_RCV_TMR bit in the RX Control Register A (RX_CTL_A).

Note:

Setting N_RETRY_CNT to zero after the GO bit has been set will have no effect for the current transfer.

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