SN260 datasheet(25/88 Pages) STMICROELECTRONICS

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SN260

SPI protocol

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6.2.7

Error conditions

If two or more different error conditions occur back to back, only the first error condition will

be reported to the Host (if it is possible to report the error). The following are error conditions

that might occur with the SN260.

●

Oversized EZSP frame

If the transaction includes an EZSP Frame, the Length Byte cannot be a value greater

than 125. If the SN260 detects a length byte greater than 125, it will drop the incoming

Command and abort the entire transaction. The SN260 will then assert nHOST_INT

after Slave Select returns to Idle to inform the Host through an error code in the

Response section what has happened. Not only is the Command in the problematic

transaction dropped by the SN260, but the next Command is also dropped, because it

is responded to with the Oversized EZSP Frame Error Response.

●

Aborted transaction

An aborted transaction is any transaction where Slave Select returns to Idle

prematurely and the SPI Protocol dropped the transaction. The most common reason

for Slave Select returning to Idle prematurely is the Host unexpectedly resetting. If a

transaction is aborted, the SN260 will assert nHOST_INT to inform the Host through an

error code in the Response section what has happened. When a transaction is

aborted, not only does the Command in the problematic transaction get dropped by the

SN260, but the next Command also gets dropped since it is responded to with the

Aborted Transaction Error Response.

●

Missing frame terminator

Every Command and Response must be terminated with the Frame Terminator byte.

The SN260 will drop any Command that is missing the Frame Terminator. The SN260

will then immediately provide the Missing Frame Terminator Error Response.

●

Long transaction

A Long Transaction error occurs when the Host clocks too many bytes. As long as the

inter-command spacing requirement is met, this error condition should not cause a

problem, since the SN260 will send only 0xFF outside of the Response section as well

as ignore incoming bytes outside of the Command section.

●

Unresponsive

Unresponsive can mean the SN260 is not powered, not fully booted yet, incorrectly

connected to the Host, or busy performing other tasks. The Host must wait the

maximum length of the Wait section before it can consider the SN260 unresponsive to

the Command section. This maximum length is 200 milliseconds, measured from the

end of the last byte sent in the Command Section. If the SN260 ever fails to respond

during the Wait section, it is valid for the Host to consider the SN260 unresponsive and

to reset the SN260. Additionally, if nHOST_INT does not assert within 10ms of nWAKE

asserting during the wake handshake, the Host can consider the SN260 unresponsive

and reset the SN260.

6.3

SPI protocol timing

Figure 6 illustrates all critical timing parameters in the SPI Protocol. These timing

parameters are a result of the SN260’s internal operation and both constrain Host behavior

and characterize SN260 operation. The parameters shown are discussed elsewhere in this

document. Note that Figure 6 is not drawn to scale, but is provided to illustrate where the

parameters are measured.

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