QT1103-ISG View Datasheet(PDF) - Quantum Research Group
Part Name
Description
Manufacturer
QT1103-ISG Datasheet PDF : 22 Pages
| |||
2.9 Simplified Mode
A simplified operating mode which does not require the
majority of option resistors is available. This mode is set by
connecting a resistor labeled SMR between pins SNS6K and
SNS7 (see Figure 1.2).
In this mode there is only one option available - AKS enable
or disable. When AKS is disabled, Fast Detect mode is
enabled; when AKS is enabled, Fast Detect mode is off.
AKS in this mode is global only (i.e. operates across all
functioning keys).
The other option features are fixed as follows:
DETECT Pin: Push-pull, active high
SYNC/LP Function: LP mode, ~110ms response time
Max On-Duration: 60 seconds
See also Tables 1.6 and 1.7.
2.10 Unused Keys
Unused keys should be disabled by removing the
corresponding Cs and Rsns components and connecting
SNS pins as shown in the ‘Unused’ column of Table 1.1.
Unused keys are ignored and do not factor into the AKS
function (Section 2.6).
2.11 Serial 1W Interface
2.11.1 Introduction
The 1W serial interface is an RS-232 based auto baud rate
serial asynchronous interface that requires only one wire
between the host MCU and the QT1103. The serial data are
extremely short and simple to interpret.
Auto baud rate detection takes place by having the host
device send a specific character to the QT1103, which allows
the QT1103 to set its baud rate to match that of the host.
Depending on the timing of a 1W host transmission, the
QT1103 device may need to abort an acquisition burst, and
rerun it after the transmission is complete and a reply has
been sent. As a consequence, each host request can
potentially result in a small, unnoticeable increase in
detection delay.
1W Connection: The 1W pin should be pulled high with a
resistor. When not in use it floats high, hence this causes no
increase in supply current.
During transmission from the host, the host may drive the 1W
line with either an open-drain or a push-pull driver. However,
if the host uses push-pull driving, it must release the 1W line
as soon as it is done with its stop bit so that there is no drive
conflict when the QT1103 sends its reply.
If open-drain transmission is used by the host, the value of
the pull-up resistor should be optimized for the desired baud
rate: faster rates require a lower value of resistor to prevent
rise-time problems. A typical value for 19,200 baud might be
100k. An oscilloscope should be used to confirm that the
resistor is not causing excessive timing skew that might
cause bit errors.
The QT1103 uses push-pull drive to transmit data out on the
1W line back to the host. When the stop bit level is
established, 1W is floated; for this reason, a pull-up resistor
should always be used on the 1W pin to prevent the signal
from drifting to an undefined state. A 100k pull-up resistor
on 1W is recommended, unless the host uses open-drain
drive to the QT1103, in which case a lower value may be
required (see prior paragraph).
2.11.2 Basic 1W Operation
The basic sequence of 1W serial operation is shown in
Figure 2.6. The 1W line is bi-directional and must be pulled
high with a resistor to prevent a floating, undefined state (see
Section 2.11.1).
One feature of this method is that the baud rate can be any
rate between 8,000 and 38,400 bits per second. Neither the
QT1103 nor the host device has to be accurate in their
transmission rates, i.e. crystal control is not required.
Oscillator Tolerance: While the auto baud rate detection
mechanism has a wide tolerance for oscillator error, the QT’s
oscillator should still not vary by more than ±20 percent from
the recommended value. Beyond a ±20 percent error,
communications at either the lower or upper stated limits
could fail. The oscillator frequency can be checked with an
oscilloscope by probing the pulse width on the SNS lines
(see Section 3.1, page 11).
Figure 2.6 Basic 1W Sequence
key state
change
request
from host
(1 byte)
driven reply
from QT1103
(2 bytes)*
1W
/CHANGE floating
floating
floating
floating
Host Request Byte: The host requests the key
state from the QT1103 by sending an ASCII "P"
character (ASCII decimal code 80, hex 0x50)
over the 1W line. The character is formatted
according to conventional RS-232:
8 data bits
no parity
1 stop bit
baud rate: 8,000 - 38,400
1W
(from host)
1 ~ 3 bit periods
*See Figure 2.8
Figure 2.7 1W UART Host Pattern
Figure 2.7 shows the bit pattern of the host
request byte (‘P’). The first bit labeled ‘S’ is the
start bit, the last ‘S’ is the stop bit. This bit pattern
should never be changed. The QT1103 will
respond at the same baud rate as the received
‘P’ character.
Serial bits
S01234567S
Lq
10
QT1103_3R0.03_0607
Share Link: 