ASAHI KASEI
[AK4181A]
BUSY and DOUT goes to “L” from Hi-Z state at the falling edge of CSN. The AK4181A latches the 8bit control word serially via
DIN at the rising edge of DCLK. As the AK4181A starts the command decoding at the first “H” bit after CSN= “↓”, MSB (S bit)
of the command must be “H”.
Tracking time is the period from the falling edge of 5th DCLK to the falling edge of 8th DCLK. If SER/ DFR = “1”, PD0= “0”,
and if analog input is X-axis or Y-axis (the measurement is the pen position or pen pressure), the touch screen driver switches are
turned ON for this 3DCLK period. If SER/ DFR = “0”, the switches are turned ON for the period from 5DCLK↓ to 20 DCLK↓.
BUSY is “H” for one DCLK period, which is from 8DCLK↓ to 9DCLK↓. BUSY is “L” for other period.
The AK4181A outputs A/D data with MSB first via DOUT from the falling edge of 9th DCLK.
DIN must keep low state for minimum 7 DCLK times (9th-15th DCLK) after command is sent on the DIN.
The AK4181A can output one A/D data per 15 DCLK clock cycles for the fastest way as shown in the dotted line of the Figure 6.
Pen Interrupt
The AK4181A has pen interrupt function to detect the pen touch. Pen interrupt function is enabled at power-down state. YN pin is
connected to GND at the PEN interrupt enabled state. And XP pin is pulled up via an internal resistor (Ri), typically 50k ohm.
PENIRQN pulled up via an external resistor, 100k ohm, is also connected to XP pin. If touch plate is pressed by pen the current
flows via <VCC> – <Ri> – <XP> –<the plates> - <YN>. The resistance of the plate is generally 1k ohm or less, PENIRQN is
forced to “L” level. If the pen is released, PENIRQN returns “H” level because two plates are disconnected, and the current
doesn’t flow via two plates.
If the plate is touched with pen or finger, PENIRQN goes to “L” at CSN = “H” unless previous command issued with both PD1
and PD0 is “1”. PENIRQN is disabled and keeps “H” level regardless of the touched/non-touched state if CSN = “H”.
The operation of PENIRQN is related to PD0 bit. PD0 bit is updated at the rising edge of 8th DCLK (please see “ Power-down
Control” for the detail). Therefore, the last PD0 bit is valid until this timing. (The internal voltage reference is controlled by only
PD1 bit regardless of PD0 bit and CSN state.)
i.
The period from the 5th DCLK↓ to the 20th DCLK↓
The behavior of PENIRQN is related to the selected analog input. If the X-axis or Y-axis is selected as analog input, PENIRQN
is forced to “L” regardless of the touched/non-touched state. If the temperature, VBAT, or auxiliary inputs is selected,
PENIRQN is forced to “H” regardless of the touched/non-touched state.
ii.
The period from CSN↓ to the 5th DCLK.
The behavior of PENIRQN is related to the combination of the last selected analog input channel, and the last PD0 bit. If the
last PD0 bit was set to “0”, PENIRQN is “H” while the plate is not pressed, and “L” while the plate is pressed regardless of the
last analog input. If the last PD0 bit was set to “1”, the last analog input decides the level of PENIRQN. If the last analog input
channel is ether X-axis or Y-axis, PENIRQN is “L” for all the time in this period regardless of the touched/non-touched state.
On the other hand, if the last analog input is temperature, VBAT, or auxiliary inputs, PENIRQN is “H” for all the time in this
period regardless of the touched/non-touched state.
iii.
The period from the 20th DCLK↓ to CSN↑
The behavior of PENIRQN is related to the combination of the current selected analog input channel, and the current PD0 bit.
If the current PD0 bit is set to “0”, PENIRQN is “H” while the plate is not pressed, and “L” while the plate is pressed regardless
of the current selected analog input. If the current PD0 bit is set to “1”, the current analog input decides the operation of
PENIRQN. If the current analog input channel is ether X-axis or Y-axis, PENIRQN is “L” for all the time in this period
regardless of the touched/non-touched state. On the other hand, if the current analog input is temperature, VBAT, or auxiliary
inputs, PENIRQN is “H” for all the time in this period regardless of the touched/non-touched state.
It is recommended that the micro controller mask the pseudo-interrupts while the control command is issued or A/D data is output.
Full power down (CSN = “H”, DIN = “H”, DCLK= “L” or “H”) should force internal register to initial value 00H and XP, YP, XN
pin to Hi-z state. In addition to this, the current does not flow even if the plate is touched with pen or finger. PENIRQN goes to
“H” regardless of pen touch at full power.
MS0313-E-00
13
2004/06
AKM [ ASAHI KASEI MICROSYSTEMS ]
