NJU6538 View Datasheet(PDF) - Japan Radio Corporation
Part Name
Description
Manufacturer
NJU6538 Datasheet PDF : 27 Pages
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NJU6538
(5-6) Power save mode
Key scan operates with follows in Power save mode.
1, Key scan signal output terminals S0 – S4 output “H”, “L” signals by the Power save mode set when key scan does not
operate (refer the detail of instructions), and output key scan signals after start of key scan operation. The conditions of
key scan signal input terminals K0 – K4 are “L” state with internal pull-down resistances, though “H” signal comes in to
K0 – K4 corresponding to the turned on keys.
2, The oscillation circuit function of key scan starts twice operations when any keys on cross points with S0– S4 terminals
line and K0 – K4 turned on. It stops when a couple of data by continuously twice key scan operations are accorded and
fixed as a correct key status. It operates more 2 times when the key status is not fixed and any keys are still turning on.
It repeats again and again until key status is fixed. The correct key status data is stored and newly key scan operation
does not start until external MPU reads data out after key status is fixed.
3, When the key status is fixed, SIO terminal outputs “L” signal as Key data read out request to MPU. MPU should read
key data out at detection of this “L” signal.
4, The Key data read out request signal is released and SIO terminal outputs “H” signal after finish of MPU key data read
out for newly key scan operation. Although Power save mode is not released.
SIO terminal requires pull up resistor because of Open drain type output. Multiple data of key are output in case
of key more input so that MPU should process the data by itself.
Key scan example (Power save mode)
Ex.) D0= ”0”, D1= ”1” (K4=“H” power save)
S0 “L”
S1 “L”
S2 “L”
S3 “L”
When some key on these lines are turned on, the
oscillation starts and Key scan starts the operation until all
of key are turned off.
*1
S4 “H”
K0
K1
K2
K3
K4
*1 These diodes are required to recognize key more input of keys on the K4 line when only K4 terminal outputs “H”
signal in power save mode as shown above example. In case of no diodes, incorrect key data may read out
sometimes by key more input of keys on lines of K0 to K4.
T=1/fsys =2/fosc
Key input
(fsys : Internal system clock frequency)
(K4)
Key scan
CE
322T[s]
322T[s]
SCL
SI
Data send
Data send
Data send
T = 1 / fosc
SO
Ver.2003-05-09
Key data read
request
Key data read
Key data read
Key data read
request
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