PCF8533 データシートの表示（PDF） - Philips Electronics
部品番号
コンポーネント説明
メーカー
PCF8533 Datasheet PDF : 36 Pages
| |||
Philips Semiconductors
Universal LCD driver for low multiplex rates
Product specification
PCF8533
6.1 Power-on reset
At Power-on the PCF8533 resets to a starting condition as
follows:
1. All backplane outputs are set to VLCD.
2. All segment outputs are set to VLCD.
3. The drive mode ‘1 : 4 multiplex with 1⁄3bias’ is selected.
4. Blinking is switched off.
5. Input and output bank selectors are reset (as defined
in Table 5).
6. The I2C-bus interface is initialized.
7. The data pointer and the subaddress counter are
cleared.
8. Display disabled.
Data transfers on the I2C-bus should be avoided for 1 ms
following Power-on to allow completion of the reset action.
6.2 LCD bias generator
Fractional LCD biasing voltages are obtained from an
internal voltage divider of the three series resistors
connected between VLCD and VSS. The centre resistor can
be switched out of the circuit to provide a 1⁄2bias voltage
level for the 1 : 2 multiplex configuration.
6.3 LCD voltage selector
The LCD voltage selector co-ordinates the multiplexing of
the LCD in accordance with the selected LCD drive
configuration. The operation of the voltage selector is
controlled by MODE SET commands from the command
decoder.
The biasing configurations that apply to the preferred
modes of operation, together with the biasing
characteristics as functions of VOP and the resulting
discrimination ratios (D), are given in Table 2.
A practical value for VOP is determined by equating Voff(rms)
with a defined LCD threshold voltage (Vth), typically when
the LCD exhibits approximately 10% contrast. In the static
drive mode a suitable choice is VOP > 3Vth.
Multiplex drive ratios of 1 : 3 and 1 : 4 with 1⁄2bias are
possible but the discrimination and hence the contrast
ratios are smaller ( 3 = 1.732 for 1 : 3 multiplex or
----3-2---1-- = 1.528 for 1 : 4 multiplex).
The advantage of these modes is a reduction of the LCD
full-scale voltage VOP as follows:
• 1 : 3 multiplex (1⁄2bias):
VOP = 6 × Voff(rms) = 2.449Voff(rms)
• 1 : 4 multiplex (1⁄2bias):
VOP = (---4-----×--3-------3----) = 2.309Voff(rms)
These compare with VOP = 3Voff(rms) when 1⁄3bias is used.
Note: VOP = VLCD.
Table 2 Preferred LCD drive modes: summary of characteristics
NUMBER OF
LCD DRIVE MODE
BACKPLANES LEVELS
LCD BIAS
CONFIGURATION
static
1
2
static
1:2
1:2
1:3
1:4
2
3
1⁄2
2
4
1⁄3
3
4
1⁄3
4
4
1⁄3
V-----oV--f--fO-(-r--mP----s--)
0
0.354
0.333
0.333
0.333
V-----oV--n--O-(-r--mP----s--)
1
0.791
0.745
0.638
0.577
D = V-V----oo--nf--f-((-rr--mm----ss--))
∞
2.236
2.236
1.915
1.732
1999 Jul 30
7
Share Link: 