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MAX6850

4-Wire Interfaced, 7-, 14-, and 16-Segment Alphanumeric Vacuum-Fluorescent Display Controller

Maxim Integrated 

4-Wire Interfaced, 7-, 14-, and 16-Segment Alpha-

numeric Vacuum-Fluorescent Display Controller

GRID 1

GRID 2

GRID 3

GRID 4

GRID 5

GRID 6

GRID 7

GRID 8

Figure 2. Example of a Two-Digit-per-Grid Display

°C °F pH mW

4 ANNUNCIATOR SEGMENTS

14-SEGMENT CHARACTER

DECIMAL POINT (DP) SEGMENT

CURSOR SEGMENT

Figure 3. Digit Structure with 14-Segment Character,

DP Segment, Cursor Segment, and Four Annunciators

MICROCONTROLLER

DOUT

SCLK

CS

MAX6850

DIN

SCLK

VFDOUT

VFCLK

CS

VFLOAD

VFBLANK

VFD TUBE DRIVER

VFDIN

VFCLK

VFLOAD

VFBLANK

GRID/

ANODE

DRIVERS

Figure 4. Connection of the MAX6850 to VFD Driver and VFD Tube

out of phase with the cursor. The blink-speed control is

software selectable to be one or two blinks per second

(OSC = 4MHz).

DP segments can be lit or off, but have no blink control.

A DP segment is set by the same command that writes

the digit’s 7-, 14-, or 16-segment character.

The cursor segment is controlled differently. A single

register selects one digit’s cursor from the entire dis-

play, and that can be lit either continuously or blinking.

All the other digits’ cursors are off.

The designations of DP, cursor, and annunciator are

interchangeable. For example, consider an application

requiring only one DP lit at a time, but the DP needs to

blink. The DP function does not have blink capability.

Instead, the DP segments on the display are routed

(using the output map) to the cursor function. In this

case, the DP segments are controlled using the cursor

register.

The output of the controller is a 4-wire serial stream that

interfaces to industry-standard, shift-register, high-volt-

age grid/anode VFD tube drivers (Figure 4). This inter-

face uses three outputs to transfer and latch grid and

anode data into the tube drivers, and a fourth output

that enables/disables the tube driver outputs (Figure 6).

The enable/disable control is modulated by the

MAX6850 for both PWM intensity control and interdigit

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