CB-ACC-36【PDF 55/58 页】ANTENNA 1/2WV 2.4GHZ 10CM RPSMA

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Version 1.17 2011-09

A.2.3.3 GREEN/Switch-1 signal

The GREEN/Switch-1 signal is a multiplexed signal:

- GREEN - Logic green LED signal (see Chapter 3, Table 14). Becomes valid 500ms af-

ter start up.

- Switch-1 - The module reads the status of the signal at startup to decide if the serial in-

terface settings shall be restored (LOW) (see the Serial Port Adapter AT Commands

specification l for more details). The input signal must be stable for the first 500ms after

startup (after reset/power on reset).

The signal is internally pulled-up (16k&) to 3.0V for NOT restoring settings to default.

Note! The internal 16k&& && pull-up is smaller than on previous product generations from

connectBlue. This requires a smaller pull-down resistor (1k&& &&) for a low state.

If a LED is used and a switch is required to be able to restore the settings, a high impend-

ence buffer need to prevent the signal from being pulled-up via the LED. A 74HC08 logic

gate can be used in a 3/3.3V system (see Figure 23) and a 74HCT08 logic gate in a 5V sys-

tem (see Figure 24).

Both gates are available in a single gate package (74AHC1G08/74AHCT1G08).

Sometimes, over time, switch contacts can get an oxide layer. This may cause the closed

switch resistance to become too high to sink the signal to logic LOW (the signal is internally

pulled-up to 16k&). A design that prevents this can be found in Figure 28.

Figure 23: Switch-1 used together with a

green LED in a 3.3V host system. The status

of the signal can also be used as input to a

host controller. Notice the 1k&

& &

& serial resistor.

Figure 24: Switch-1 used together with a green

LED in a 5V host system. The status of the

signal can also be used as input to a host

controller. Notice the 1k&

& &

& serial resistor.

The buffer can be removed in a 3.3V system if no restore switch is required (see Figure 25).

In a 5V system the high state output (2.8V) from the module is not enough to turn off the

LED, so a 74HCT08 buffer can be used to raise the high level to 5V (see Figure 26).

The 74HCT08 gate is also available in a single gate package (74AHCT1G08).

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