SIO1007 datasheet(42/108 Pages) MICROCHIP

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SIO1007

DS00002020A-page 42

 2005 - 2015 Microchip Technology Inc.

12.1.1

SER_IRQ CYCLE CONTROL

There are two modes of operation for the SER_IRQ Start Frame.

1) Quiet (Active) Mode: Any device may initiate a Start Frame by driving the SER_IRQ low for one clock, while the

SER_IRQ is Idle. After driving low for one clock the SER_IRQ is immediately tri-stated without at any time driving high.

A Start Frame may not be initiated while the SER_IRQ is Active. The SER_IRQ is Idle between Stop and Start Frames.

The SER_IRQ is Active between Start and Stop Frames. This mode of operation allows the SER_IRQ to be Idle when

there are no IRQ/Data transitions which should be most of the time.

Once a Start Frame has been initiated, the Host Controller will take over driving the SER_IRQ low in the next clock and

will continue driving the SER_IRQ low for a programmable period of three to seven clocks. This makes a total low pulse

width of four to eight clocks. Finally, the Host Controller will drive the SER_IRQ back high for one clock, then tri-state.

Any SER_IRQ Device (i.e., The SIO1007) which detects any transition on an IRQ/Data line for which it is responsible

must initiate a Start Frame in order to update the Host Controller unless the SER_IRQ is already in an SER_IRQ Cycle

and the IRQ/Data transition can be delivered in that SER_IRQ Cycle.

2) Continuous (Idle) Mode: Only the Host controller can initiate a Start Frame to update IRQ/Data line information. All

other SER_IRQ agents become passive and may not initiate a Start Frame. SER_IRQ will be driven low for four to eight

clocks by Host Controller. This mode has two functions. It can be used to stop or idle the SER_IRQ or the Host Controller

can operate SER_IRQ in a continuous mode by initiating a Start Frame at the end of every Stop Frame.

An SER_IRQ mode transition can only occur during the Stop Frame. Upon reset, SER_IRQ bus is defaulted to Contin-

uous mode, therefore only the Host controller can initiate the first Start Frame. Slaves must continuously sample the

Stop Frames pulse width to determine the next SER_IRQ Cycle’s mode.

12.1.2

SER_IRQ DATA FRAME

Once a Start Frame has been initiated, the SIO1007 will watch for the rising edge of the Start Pulse and start counting

IRQ/Data Frames from there. Each IRQ/Data Frame is three clocks: Sample phase, Recovery phase, and Turn-around

phase. During the Sample phase, the SIO1007 drives the SER_IRQ low, if and only if, its last detected IRQ/Data value

was low. If its detected IRQ/Data value is high, SER_IRQ is left tri-stated. During the Recovery phase, the SIO1007

drives the SER_IRQ high, if and only if, it had driven the SER_IRQ low during the previous Sample Phase. During the

Turn-around Phase, the SIO1007 tri-states the SER_IRQ. The SIO1007 will drive the SER_IRQ line low at the appro-

priate sample point if its associated IRQ/Data line is low, regardless of which device initiated the Start Frame.

The Sample Phase for each IRQ/Data follows the low to high transition of the Start Frame pulse by a number of clocks

equal to the IRQ/Data Frame times three, minus one. (e.g. The IRQ5 Sample clock is the sixth IRQ/Data Frame, (6 x 3)

- 1 = 17th clock after the rising edge of the Start Pulse).

TABLE 12-1:

SER_IRQ SAMPLING PERIODS

SER_IRQ Period

Signal Sampled

# of Clocks Past Start

Not Used

2IRQ1

nIO_SMI/IRQ2

4IRQ3

5IRQ4

6IRQ5

7IRQ6

8IRQ7

9IRQ8

IRQ9

IRQ10

IRQ11

IRQ12

IRQ13

IRQ14

IRQ15

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