EM260-RTR datasheet(24/50 Pages) SILICONIMAGE

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EM260

120-0260-000M Rev 1.1

Page 24

5.2.5

Spacing

To ensure that the EM260 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 EM260 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 EM260 is ready to accept a command.

5.2.6

Waking the EM260 from Sleep

Waking up the EM260 involves a simple handshaking routine as illustrated in Figure 6. This handshaking insures

that the Host will wait until the EM260 is fully awake and ready to accept commands from the Host. If the

EM260 is already awake when the handshake is performed (such as when the Host resets and the EM260 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.

Note: nWAKE should not be asserted after the EM260 has been reset until the EM260 has fully booted, as

indicated by the EM260 asserting nHOST_INT. If nWAKE is asserted during this boot time, the EM260 may enter

bootloader mode. See section 5.6.1, Bootloading the EM260.

Figure 6. EM260 Wake Sequence

Waking the EM260 involves the following steps:

1. Host asserts nWAKE.

2. EM260 interrupts on nWAKE and exits sleep.

3. EM260 performs all operations it needs to and will not respond until it is ready to accept commands.

4. EM260 asserts nHOST_INT within 300ms of nWAKE asserting. If the EM260 does not assert nHOST_INT

within 300ms of nWAKE, it is valid for the Host to consider the EM260 unresponsive and to reset the

EM260.

5. Host detects nHOST_INT assertion. Since the assertion of nHOST_INT indicates the EM260 can accept SPI

transactions, the Host does not need to hold Slave Select high for the normally required minimum 1ms of

inter-command spacing.

6. Host deasserts nWAKE after detecting nHOST_INT assertion.

7. EM260 will deassert nHOST_INT within 25μs of nWAKE deasserting.

8. After 25μs, any change on nHOST_INT will be an indication of a normal asynchronous (callback) event.

5.2.7

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

EM260.

Unsupported SPI Command: If the SPI Byte of the command is unsupported, the EM260 will drop the incoming

command and respond with the Unsupported SPI Command Error Response. This error means the SPI Byte is

nHOST_INT

nWAKE

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