at42qt1481 ATMEL Corporation, at42qt1481 Datasheet - Page 49

• Manufacturer Part Number: at42qt1481
• Description: 48-key Qmatrix Ic
• Manufacturer: ATMEL Corporation

5.20
9621B–AT42–06/11
STATUS Output – STS
This function is programmed on a global basis.
KGTT Default value: 7 (32)
KGTT Possible range: 0 – 15 (4 – 64)
The STATUS pin is designed to be used as a status and error signaling mechanism for the host
controller.
One use for this pin is to alert the host that there is key activity, in order to limit the amount of
communication between the QT1481 and the host. The STATUS pin should ideally be connected
to an interrupt pin on the host that can detect an edge, following which the host can proceed to
poll the QT1481 for further information.
The STATUS pin is an open-drain output with an internal 20 k – 50 k pull-up resistor. This
allows multiple devices to be connected together in a single wire-OR logic connection with the
host. When the STATUS pin becomes active, the host can poll all devices to identify which one is
reporting.
Table 5-5 on page 55
become active. Except for STS_DEBUG, the various items in the table are logical-OR'd
together.
STS_TOUCH: When this option (STS, bit 5) is enabled, the STATUS output can be used to alert
the host of touch changes. The STATUS output becomes active after reset and when there is a
change in key state (either touch or touch release). It does not self-clear but becomes inactive
again only after the host issues command 0x06. After the host has issued command 0x06, the
STATUS output becomes inactive at the end of the matrix scan provided that there are no keys in
detect and there are no other conditions demanding it be active. To avoid missing touches and
future STATUS assert edges, the host should issue further 0x06 commands until STATUS
becomes inactive.
STS_DEBUG: When this option is enabled (STS, bit 7, See
streams one frame of data out of the Debug port after each matrix scan. When STS_DEBUG is
enabled it impacts the key response time because the next matrix scan is delayed until the
debug frame has been fully transmitted. To prevent interference, this bit should be used
exclusively, and not in conjunction with any other bit.
STS_RSTHOST: The STATUS pin can even be used as a watchdog for the host, to reset it
should the host fail to send regular transmissions to the QT1481 (bit 0 of STS byte). The comms
timeout required to generate the reset signal is about 2 seconds of inactivity. If this feature is
enabled, it does not become effective until the first command is received from the host;
therefore, it is assumed that there is at least some initial host activity for this feature to work.
Note:
STS Default value: 0x20 (STS_TOUCH)
1. The STATUS output is preserved during sleep.
2. To prevent interference, STS_DEBUG should not be enabled with any other item.
3. The reset pulse should be allowed to complete before the host sends commands to
the QT1481. If commands are received from the host while STATUS is low, STATUS
will remain low until the commands stop and the 2s internal host reset timer is
allowed to fully cycle.
shows the possible internal conditions that can cause the STATUS pin to
Section B on page
AT42QT1481
65), the QT1481
49