HT49CA1 View Datasheet(PDF) - Holtek Semiconductor
Part Name
Description
MFG CO.
'HT49CA1' PDF : 58 Pages View PDF
HT49RA1/HT49CA1
LCD Driver Output
The number of COM and SEG outputs supplied by the
LCD driver, as well as its biasing and duty options, are
dependent upon the configuration options selected. The
accompanying table lists the various options for each of
the devices.
Duty
1/2
1/3
1/4
Driver
Number
33´2
33´3
32´4
Bias
1/2 or 1/3
1/2 or 1/3
1/2 or 1/3
Bias
Type
C type
C type
C type
LCD Driver Outputs, Duty and Bias Options
The nature of Liquid Crystal Displays require that only
AC voltages can be applied to their pixels as the applica-
tion of DC voltages to LCD pixels will cause permanent
damage. For this reason the relative contrast of an LCD
display is controlled by the actual RMS voltage applied
to each pixel, which is equal to the RMS value of the
voltage on the COM pin minus the voltage applied to the
SEG pin. This differential RMS voltage must be greater
than the LCD saturation voltage for the pixel to be on
and less than the threshold voltage for the pixel to be off.
The requirement to limit the DC voltage to zero and to
control as many pixels as possible with a minimum num-
ber of connections, requires that both a time and ampli-
tude signal is generated and applied to the application
LCD. These time and amplitude varying signals are au-
tomatically generated by the LCD driver circuits in the
microcontroller. What is known as the duty determines
the number of common lines used, which are also
known as backplanes or COMs. The duty, which is cho-
sen by a configuration option to have a value of 1/2, 1/3
or 1/4 and which equates to a COM number of 2, 3 and 4
respectively, therefore defines the number of time divi-
sions within each LCD signal frame. The accompanying
timing diagrams depict the LCD signals generated by
the microcontroller for various values of duty and bias.
D u r in g R e s e t o r in H A L T M o d e
VA
C O M 0,C O M 1
VB
VSS
VA
A ll s e g m e n t o u tp u ts
VB
VSS
N o r m a l O p e r a tio n M o d e
1 F ra m e
VA
COM 0
VB
VSS
VA
COM 1
VB
VSS
VA
A ll s e g m e n ts O F F
VB
VSS
VA
C O M 0 s e g m e n ts O N
VB
VSS
VA
C O M 1 s e g m e n ts O N
VB
VSS
VA
A ll s e g m e n ts O N
VB
VSS
LCD Driver Output (1/2 Duty, 1/2 Bias)
Note For 1/2 Bias, the VA=VLCD and VB=VLCD´1/2
The LCD function can be optioned as on or off during the Power Down Mode by a configuration option.
Rev. 1.10
19
March 30, 2014
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