If SM is set for idle-low SCK:
Data is shifted out
of the QT300 on the rising edge of SCK and should
be shifted into the host on the falling edge of SCK.
If SM is set for idle-high SCK:
Data is shifted out
of the QT300 on the falling edge of SCK and
should be shifted into the host on the rising edge of
SCK.
The maximum clock speed is 40kHz, and the
timings should obey the parameters Tskh and Tskl
in Table 7-2.
/DRDY
- Data Ready (Optional); active low output
only. This indicates to the host that the device is
ready to send data back to the host. During idle
times this pin floats and therefore must be
connected to a pullup resistor.
The DRDY line can be used as a Slave Select line
(SS). The host does not need this line to operate in
many cases. DRDY can be used to 'frame' byte
transmissions.
Between bytes /DRDY will go high for a period
determined by the MLS setup parameter; the
minimum period is 8.3µs.
A typical Master mode SPI sequence is:
1) Host pulses /REQ low for
≥30µs.
2) QT300 acquires a signal in response to /REQ.
3) QT300 pulls /DRDY low when ready to send data.
4) Host detects /DRDY low and prepares to receive
data.
5) QT300 clocks out first byte of data (MSB).
6) QT300 sets /DRDY high for a duration determined
by Setup parameter MLS.
7) QT300 pulls /DRDY low.
Figure 4-1 UART and Trigger Pulse Signal.
overrun. The default value is 148 (resulting in a 500µs gap).
The relationship is:
Tmls (in
µs)
= (10 + MLS x 4) / 1.2
Where MLS = 0..255 (from user setup MLS)
Master SPI mode requires at least 3 signals to operate:
/REQ
- Request Acquisition Input; Active low input-only.
When /REQ is pulled low, the QT300 wakes and starts an
acquire. The IC will transmit the resulting data only when
the acquire has finished.
/REQ must return high before the end of the burst.
If
/REQ is still low at the end of the burst the part goes into
Setup mode. The minimum duration of /REQ is 30µs.
SDO
- Serial Data Output; Idle low output-only. This is the
data output to the host during an SPI transfer. When not in
use, this pin floats. This pin should be connected to the
SDI input pin of the host device.
SCK
- SPI clock; Idle high or idle low, output-only. The idle
state is determined in Setups by the serial mode (SM)
parameter.
8) QT300 clocks out the low byte (LSB).
9) QT300 releases /DRDY to float high.
4 Serial 1W UART Interface
The single wire ('1W') UART interface allows all
communications to take place over a single bidirectional line
with a 10K pullup resistor. The host device triggers the
QT300 to acquire by means of a pulse sent to the QT300
over the wire. The Baud rate is established by the width of
this pulse; the pulse width establishes the bit rate of the
UART transmission to follow. The QT300 then acquires, and
responds by sending two bytes of data back over the 1W line
with a delay between the bytes as determined by parameter
MLS.
1W operation permits a device to be controlled from a single
pin on a host controller, using either a hardware or software
UART. Several QT300’s can coexist on a single host pin,
provided there is some logic steering.
This mode is set via the cloning process using parameter SM
(see Section 6).
LQ
5
QT300 R1.02/0204
QUANTUM [ QUANTUM RESEARCH GROUP ]
