MAX6852 MAXIM [Maxim Integrated Products], MAX6852 Datasheet - Page 20

• Manufacturer Part Number: MAX6852
• Description: 4-Wire Interfaced, 5 x 7 Matrix Vacuum- Fluorescent Display Controller
• Manufacturer: MAXIM [Maxim Integrated Products]

4-Wire Interfaced, 5
Fluorescent Display Controller
The multiplex clock frequency determines the multiplex
scan rate and the blink timing. The display scan rate is
{OSC / 400 / (1 + grids register value)}. There are 400
OSC cycles per digit multiplex period. For example,
with OSC = 4MHz, each display digit is enabled for
100µs. For a 40-grid display tube (grids register value
= 39 or 0x27), the display scan rate is 250Hz.
The BLINK output is the selectable blink period clock. It
is nominally 0.5Hz or 1Hz (OSC = 4MHz). It is low dur-
ing the first half of the blink period, and high during the
second half. The PORT0 and PORT1 general-purpose
outputs may be programmed to be BLINK output.
Synchronize the BLINK timing if desired by setting the
T bit in the configuration register (Table 19).
The RC oscillator uses an external resistor R
an external capacitor C
quency. R
connects from OSC1 to ground. The recommended val-
ues of R
which makes the BLINK frequencies 0.5Hz and 1 Hz:
f
where:
K
R
80kΩ)
C
C
typically 2pF
For OSC = 4MHz, R
Table 8. Memory Mapping of User-Defined Font Register 0x05
Table 9. Font Pointer Address Behavior
20
OSC
F
OSC
COMMAND
OSC
STRAY
FONT POINTER
ADDRESS
= 2320
0x80 to 0xF6
0xF8 to 0xFF
ADDRESS
0x85
0x05
0x05
______________________________________________________________________________________
= K
= external resistor in kΩ (allowable range 8kΩ to
= external capacitor in pF
0xF7
= stray capacitance from OSC1 to GND in pF,
F
OSC
OSC
/ (R
OSC
and C
REGISTER
connects from OSC2 to ground. C
0x00–0x7F
0x00–0x7F
0x80–0xFF
DATA
Valid range to set the font address pointer. Pointer autoincrements after a font data read or write, while pointer
address remains in this range.
Further font data is ignored after a font data read or write to this pointer address.
Invalid range to set the font address pointer. Pointer is set to 0x80.
x [C
OSC
OSC
OSC
is 10kΩ and C
OSC
set the oscillator to 4MHz,
+ C
READ OR
to set the oscillator fre-
WRITE
STRAY
Read
Write
Write
]) MHz
OSC
Read 7-bit user-definable font data entry from current font address. MSB of the
register data is clear. Font address pointer is incremented after the read.
Write 7-bit user-definable font data entry to current font address. Font address
pointer is incremented after the write.
Write font address pointer with the register data.
is 56pF.
OSC
✕
OSC
and
7 Matrix Vacuum-
The effective value of C
external capacitor used, but also the stray capacitance
from OSC1 to GND. This capacitance is usually in the
1pF-to-5pF range, depending on the layout used.
The allowed range of f
set too high, the internal oscillator can stop working. An
internal fail-safe circuit monitors the multiplex clock and
detects a slow or nonworking multiplex clock. When a
slow or nonworking multiplex clock is detected, an
internal fail-safe oscillator generates a replacement
clock of about 200kHz. This backup clock ensures that
the VFD is not damaged by the multiplex operation halt-
ing inadvertently. The scan rate for 16 digits is about
15Hz in fail-safe mode, and the display flickers. A flick-
ering display is a good indication that there is a prob-
lem with the multiplex clock.
The MAX6852 operates from a single 2.7V to 3.6V
power supply. Bypass the power supply to GND with a
0.1µF capacitor as close to the device as possible. Add
a bulk capacitor (such as a low-cost electrolytic 1µF to
22µF) if the MAX6852 is driving high current from any of
the general-purpose output ports.
ACTION
FUNCTION
OSC
OSC
is 2MHz to 8MHz. If f
includes not only the actual
Power Supplies
OSC
is