QT1100A-ISG Datasheet PDF - Quantum Research Group

QT1100A-ISG View Datasheet(PDF) - Quantum Research Group

Part Name

Description

Manufacturer

QT1100A-ISG

10 KEY QTOUCH™ SENSOR IC

Quantum Research Group

QT1100A-ISG Datasheet PDF : 42 Pages

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former can occur if the Cs capacitor fails or there is a short

in the SNS circuit; if this happens, the affected key is shut

down immediately and the key is switched off.

Keys that are intentionally disabled will not burst, and so

cannot show an error. In standalone mode with no EEPROM

present (Scanport mode), keys are disabled by strapping the

SNS pins to ‘unused’ settings (Table 1.1 page 4), and this

will not generate a ‘major error’, unless the error occurs after

the part has gone through power-up calibration successfully

without detecting that the key is disabled via SNS pin

configuration.

In any mode that uses an EEPROM or uses either UART or

SPI communications, keys must be disabled by setting the

NTHR parameter to zero for the key(s) (Section 4.1). If in

EEPROM or serial mode a key is disabled via SNS pin wiring

only, it will be classified as a ‘major error’.

control. The UART mode operates in the same way and with

the same protocol and commands as the SPI interface.

UART mode is selected by strapping the CMODE pin low.

UART mode and Scanport mode can operate together. If

only UART mode is desired, the Scan_In pins need to be

grounded. If only the Scanport is used, the UART can be

ignored. An unused RX line should be connected directly to

Vdd.

UART transmission parameters are (Fosc = 12MHz):

Baud rate options:

Start bits:

Data bits:

Parity:

Stop bits:

4800, 9600, 19.2K, 28.8K

None

UART Operation with Scanport: Scanport and UART

operation can be used together. (See Section 2.14)

3 Serial Operation

There are two serial interfaces in the QT1100A: UART, and

SPI.

UART provides a simple solution using well known

asynchronous signalling. Many MCUs contain UART or

USART blocks which are perfectly suited to this mode.

MCUs without a UART hardware function can easily use a

firmware UART function in most cases. The chief advantage

of UART mode is wiring simplicity: only 3 wires, (TX, RX, and

CRDY) are required.

SPI communications are based on the well known

synchronous interface used extensively between

microcontrollers and peripherals. The QT1100A uses

slave-only SPI mode. This interface does not require an

accurate clock rate, and can operate faster than UART

mode. However, SPI operation requires 5 wires.

The host device always initiates communications

sequences; the QT1100A is incapable of chattering data

back to the host. A command from the host to the QT1100A

always ends in a one or more byte response from the

QT1100A. Some transmission types from the host require

the use of a CRC check byte to provide for robust

communications. This command/response design is

intentional for FMEA purposes so that the host always has

total control over the communications with the QT1100A.

Effectively this behavior forces designs to have inherently

self-checking ‘loop back’ characteristics.

System Response Time: The setting of the two detection

integrators (see Section 4.9) strongly affects the basic

device response time. The serial poll rate adds to this

response time. If the basic QT1100A response time is 80ms,

and the host polls the device every 50ms, the total response

time can be a very slow 130ms. Normally, the host should

poll the QT1100A every ~10ms to minimize delay ‘stacking’.

To minimize delays further, the command 0xC9 can be used

(‘Quick 1st Key’; see Section 3.5.14) instead of 0xC0.

One way to improve speed while minimizing host activity is

to have the host monitor the LED/STAT pin, perhaps via

interrupt, and service the device with a 0xC0 or 0xC9

command only when the LED/STAT pin becomes active.

(See Section 4.8)

3.1 UART Interface

UART mode allows a host device to communicate

conveniently over two serial wires asynchronously, with a

handshaking line (CRDY) to provide bidirectional data flow

3.1.1 TX Pin

The TX pin has an open-drain drive to allow bussing with

other similar parts. The TX line can thus be shared with other

UART based peripherals such as a second QT1100A.

TX must be pulled high to Vdd with a resistor in UART mode.

The resistor value will depend on the total amount of stray

capacitance on TX - more capacitance will require lower

values of pull-up resistor, especially at higher Baud rates.

The risetime of the signals on this line should be 1/10th of

the bit width, i.e., if running at 9600 Baud, the bit width is

about 100µs, and the risetime should be 10µs or less. In

most cases, a 47K resistor is low enough, however this

should be confirmed using an oscilloscope.

An unused TX pin should be connected to Vss.

3.1.2 Sleep/Wake Operation in UART Mode

The device can be put into sleep mode with a serial

command (0x05). The device can sleep for up to 700ms;

some time after this it will self-reset. The Wake and RX

functions are on the same pin, which allows a host to

conveniently wake the device with a dummy character (e.g.

0x00 null) before communicating with it. Wake operates on

the falling edge; the negative-going level must be at least

40µs wide to be recognized.