SN260 datasheet(24/88 Pages) STMICROELECTRONICS

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SPI protocol

SN260

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backup of data in the SN260. The SN260 will de-assert the nHOST_INT signal after

receiving a byte on the SPI. Due to inherent latency in the SN260, the timing of when the

nHOST_INT signal returns to idle can vary between transactions. nHOST_INT will always

return to idle for a minimum of 10µs before asserting again. If the SN260 has more output

available after the transaction has completed, the nHOST_INT signal will assert again after

Slave Select is de-asserted and the Host must make another request.

6.2.5

Spacing

To ensure that the SN260 is always able to deal with incoming commands, a minimum inter-

command spacing is defined at 1ms. After every transaction, the Host must hold the Slave

Select high for a minimum of 1ms. The Host must respect the inter-command spacing

requirement, or the SN260 will not have time to operate on the command; additional

commands could result in error conditions or undesired behavior. If the nHOST_INT signal

is not already asserted, the Host is allowed to use the Wake handshake instead of the inter-

command spacing to determine if the SN260 is ready to accept a command.

6.2.6

Waking the SN260 from sleep

Waking up the SN260 involves a simple handshaking routine as illustrated in Figure 5. This

handshaking ensures that the Host will wait until the SN260 is fully awake and ready to

accept commands from the Host. If the SN260 is already awake when the handshake is

performed (such as when the Host resets and the SN260 is already operating), the

handshake will proceed as described below with no ill effects.

Note:

A wake handshake cannot be performed if nHOST_INT is already asserted.

Figure 5.

SN260 wake sequence

Waking the SN260 involves the following steps:

Host asserts nWAKE.

SN260 interrupts on nWAKE and exits sleep.

SN260 performs all operations it needs to and will not respond until it is ready to accept

commands.

SN260 asserts nHOST_INT within 10ms of nWAKE asserting. If the SN260 does not

assert nHOST_INT within 10ms of nWAKE, it is valid for the Host to consider the

SN260 unresponsive and to reset the SN260.

Host detects nHOST_INT assertion. Since the assertion of nHOST_INT indicates the

SN260 can accept SPI transactions, the Host does not need to hold Slave Select high

for the normally required minimum 1ms of inter-command spacing.

Host de-asserts nWAKE after detecting nHOST_INT assertion.

SN260 will de-assert nHOST_INT within 25s of nWAKE de-asserting.

After 25µs, any change on nHOST_INT will be an indication of a normal asynchronous

(callback) event.

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