QT1100A-ISG View Datasheet(PDF) - Quantum Research Group
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QT1100A-ISG Datasheet PDF : 42 Pages
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is they persist even after the hardware problem is cleared,
and are only re-evaluated when the key(s) or device is
recalibrated or reset.
The error bits are the logical-OR of any error type for each
key, i.e. either a Cal error or a running key error. Errors
resulting from CRC checks and SYNC errors are not
contained in this command. The valid range of reporting is
from 0..0x03FF (i.e. the bottom 10 bits).
A CRC byte is appended to the response ; this CRC includes
the command 0xC5 itself as the first byte in the CRC
calculation.
3.5.11 Internal Code - 0xC6
This command returns an internal diagnostic code for use by
Quantum.
A CRC byte is appended to the response ; this CRC includes
the command 0xC6 itself as the first byte in the CRC
calculation.
3.5.12 Return Last Command - 0xC7
This command returns the last received command character,
in first complement (inverted). If the command is repeated
twice or more, it will return the first complement of 0xC7 i.e.
0x38.
If a prior command was not valid or was corrupted, it will
return the bad command (inverted) as well.
When this command is used immediately after command
0xC2 it will reset any active, clearable Device Status flags -
see Section 3.5.7, above.
No CRC is appended to the response.
3.5.13 Dump Setups Block - 0xC8
This command causes the device to dump the entire Setups
block back to the host.
A CRC is appended to the response but this CRC is the
same as the RAM or Setups block CRC, i.e. the command
0xC8 is not folded into the CRC calculation, only the Setups
data are used in the calculation.
3.5.14 Quick Report First Key - 0xC9
This command is virtually identical to the Report First Key
command 0xC0 (see Section 3.5.5), but does not append a
CRC, giving a simpler 1-byte response than offered by 0xC0.
This command can be used to speed up the communication
between the host and the QT1100A chip when used as the
predominant query command.
For FMEA purposes, if this command does report an active
key, then the 0xC0 command (and others) can be issued
subsequent to the 0xC9 to validate the result. In many
cases, FMEA checking is not required, and the single-byte
response of 0xC9 is sufficient.
3.6 Command Sequencing
To interface with a host, the flow diagram of Figure 3-1 is
suggested. The Setups block should normally just use the
default settings except where changes are specifically
required, such as for sensiti vity, timing, or AKS changes.
The circles in this drawing are communications interchanges
between host and sensor. The rectangles are internal host
states or processing events. A communications failure
occurs when the device fails to respond in the allotted time,
the response CRC is incorrect, or the response is
inappropriate. In these cases the host should just repeat the
command.
The control flow will spend 99% of its time alternating
between the two states within the dashed rectangle. If a key
is detected, the control flow will enter ‘Key Detection
Processing’. An enhancement might be the substitution of
the 0xC9 command for the 0xC0 command to reduce
communications overhead, at least for times when the part is
not sensing any touches.
The ‘Stuck Key Detected’ branch (bottom left) is optional,
since the device contains the max on-duration timeout
function and so can recalibrate the stuck key automatically.
However, the host can recalibrate stuck keys with greater
flexibility if the recalibration timeouts are set to infinite and
the host recalibrates them under specific conditions.
Error handling takes place whenever an error flag is
detected, or the device stops communicating (not shown).
The error handling procedure is up to the designer, however
normally this would entail shutting down the product if the
error is serious enough (for example, a key has failed).
In serial systems with an EEPROM, it is not necessary to
send the Setups block to the QT1100A each time, as the
Setups will be stored locally. However it is prudent to check
the EEPROM CRC to be sure it has not become corrupted.
The ‘Last Command’ command can be used at any time to
clear comms error flags and to resynchronize failed
communications, for example due to timing errors etc.
LQ
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Copyright © 2003-2005 QRG Ltd
QT1100A-ISG R3.02/1105
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