Matrix LED Display Driver

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15

set to an out-of-range address by writing data in the 0xF8

to 0xFF range, then address 0x80 is set instead (Table

17).

Table 18 shows the user-definable font pointer base

addresses.

Table 19 shows an example of data (characters 0, 1,

and 2) being stored in the first three user-defined font

locations, illustrating the orientation of the data bits.

Table 20 shows the six sequential write commands

required to set a MAX6953's font character RAM02 with

the data to display character 2 given in the font RAM

illustration above.

Multiplex Clock and Blink Timing

(to use the internal RC multiplex oscillator), or driven by

an external clock. The multiplex clock frequency deter-

mines the multiplex scan rate and the blink timing. The

display scan rate (the frequency that the complete four-

digit display is updated) is calculated by dividing the

frequency at OSC by 5600. With OSC at 4MHz, each

digit row is enabled for 100µs, and the display scan

rate is 714.29Hz.

The on-chip oscillator may be accurate enough for

applications using a single device. If an exact blink rate

is required, use an external clock ranging between

1MHz and 8MHz to drive OSC. The OSC inputs of mul-

tiple MAX6953s can be tied together to a common

external clock to make the devices blink at the same

rate. The relative blink phasing of multiple MAX6953s

can be synchronized by setting the T bit in the configu-

ration register for all the devices in quick succession

(Table 12).

Blink Output

The blink output pin indicates the blink phase, and is

high during the P0 period and low during the P1 period.

Blink phase status can also be read back as the P bit in

the configuration register (Table 14). Typical uses for

this output are:

• To provide an interrupt to the processor so that seg-

ment data can be changed synchronous to the

blinking. For example, a clock application may have

colon segments blinking every second between

hours and minute digits, and the minute display is

best changed in step with the colon segments. Also,

if the rising edge of blink is detected, there is half a

blink period to change the P1 digit data. Similarly, if

the falling edge of blink is detected, the user has

half a blink period to change the P0 digit data.

• If OSC is driven with an accurate frequency, blink

can be used as a seconds counter or similar.

Scan-Limit Register

The scan-limit register sets how many monocolor digits

are displayed, either two or four. A bicolor digit is con-

nected as two monocolor digits (Table 21).

ADDRESS CODE

(HEX)

REGISTER

DATA

OR WRITE

FUNCTION

0x05

0x00–0x7F

Read

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.

0x05

0x00–0x7F

Write

Write 7-bit user-definable font data entry to current font

address. Font address pointer is incremented after the write.

0x05

0x80–0xFF

Write

Write font address pointer with the register data.

Table 16. Memory Mapping of User-Defined Font Register 0x05

FONT POINTER ADDRESS

ACTION

0x80 to 0xF6

Valid range to set the font address pointer. Pointer autoincrements after a font data read or

write, while pointer address remains in this range.

0xF7

Font address resets to 0x80 after a font data read or write to this pointer address.

0xF8 to 0xFF

Invalid range to set the font address pointer. Pointer is set to 0x80 if address.

Table 17. Font Pointer Address Behavior