Cypress Semiconductor FX2LP Technical Information PDF herunterladen (Seite 280)

EZ-USB FX2 Technical Reference Manual

Page 13-6 EZ-USB FX2 Technical Reference Manual v2.1

Figure 13-5. I/O-Pin Logic when Alternate Function is an INPUT

Figure 13-5 shows an I/O pin whose alternate function is always an input.

In Figure 13-5a, the I/O pin is configured for general-purpose I/O. There’s an important difference

between alternate-function

inputs

and the alternate-function

outputs

shown earlier in Figure 13-4:

Alternate-function inputs are never disconnected; they’re always listening.

If the alternate function’s interrupt is enabled, signals on the I/O pin may trigger that interrupt. If the

pin is to be used only for general-purpose I/O, the alternate function’s interrupt must be disabled.

For example, suppose the PE5/INT6 pin is configured for general-purpose I/O. Since the INT6

function is an input, the pin signal is also routed to the FX2’s internal INT6 logic. If the INT6 inter-

rupt is enabled, traffic on the PE5 pin will trigger an INT6 interrupt. If this is undesirable, the INT6

interrupt should be disabled.

Of course, this side-effect can be useful in certain situations. In the case of PE5/INT6, for exam-

ple, PE5 can trigger an INT6 interrupt even if the I/O pin is configured as an output (i.e., OEE.5 =

1), so the FX2’s firmware can directly generate “external” interrupts.

In Figure 13-5b, the I/O pin is configured as an alternate-function input. Just as with alternate-

function outputs, the IOx/OEx output buffer is disconnected from the I/O pin, so writes to IOx and

OEx have no effect on the I/O pin. Reads from IOx, however, continue to work normally; the state

of the I/O pin (and, therefore, the input to the alternate function) is always available.

OEx Bit

IOx Bit

I/O Pin

Read

Write

Alternate Function

(Input)

OEx Bit

IOx Bit

I/O Pin

Read

Write

Alternate Function

(Input)

a) General-Purpose I/O Configuration b) Alternate-Function Configuration

1 2 ... 275 276 277 278 279 280 281 282 283 284 285 ... 459 460

Keine Kommentare

Cypress Semiconductor FX2LP Technical Information Seite 280