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MAX6955

2-Wire Interfaced, 2.7V to 5.5V LED Display Driver with I/O Expander and Key Scan

Maxim Integrated 

MAX6955

2-Wire Interfaced, 2.7V to 5.5V

LED Display Driver with I/O

Expander and Key Scan

Table 5. MAX6955 Address Map

MPeINsCsOaNgNeECFToIOrmN at for ReaDEdVinICgE ADDRESS

TsthoerAeDMd1AcXo6m95mA5aDn0isdrebayAdt6e uassAin5agdtdhAre4esMsAApX3o6i9n5tAe52r’,s tihnAet1esrnaamAl0ley

waGy NthDe stoGreNdD com1man1d byt0e is 0used0as a0ddre0ss

poiGntNeDr for a wVr+ite. Th1e poin1ter g0enera0lly au0toincr0emen1ts

afteGrNeDach daStDaAbyte 1is rea1d usin0g the0sam0e rule1s as f0or

aurwinGrgiNteDth(TeaMblAeSXC66L).9T5h5u’s1s,caomre1madanisd0 inbiytitae0tebdybp0yefrirfsotr1mcoinngfi1ga-

writeV+(FigureG7N)D. The 1mast1er ca0n now0 read1 n co0nsec0u-

tive Vb+ytes froVm+ the M1 AX61955, 0with t0he fir1st da0ta by1te

beinVg+ read fSroDmA the1regis1ter ad0 dres0sed b1y the1 initia0l-

iazfetdeVrc-+womritmeavnSedCrLibfiycteat1(iFoing,urr1ees9e).t0Wthheen0copmermf1oramnidn1gbryetae1d’s-

addSrDeAss becGaNuDse the1 store1d by0te ad1dress0 gene0rally0is

autoSiDnAcremenVte+d afte1r the w1 rite (0Table1 6). 0 0 1

SDA

SDA 1 1 0 1 0 1 0

SDA

SCL 1 1 0 1 0 1 1

SCL

GND 1 1 0 1 1 0 0

SCL

V+

1101101

SCL

SDA 1 1 0 1 1 1 0

SCL

SCL 1 1 0 1 1 1 1

Operation with Multiple Masters

If the MAX6955 is operated on a 2-wire interface with

multiple masters, a master reading the MAX6955

should use a repeated start between the write, which

sets the MAX6955’s address pointer, and the read(s)

that takes the data from the location(s). This is because

it is possible for master 2 to take over the bus after

master 1 has set up the MAX6955’s address pointer but

before master 1 has read the data. If master 2 subse-

quently changes the MAX6955’s address pointer, then

master 1’s delayed read may be from an unexpected

location.

Command Address Autoincrementing

Address autoincrementing allows the MAX6955 to be

configured with the shortest number of transmissions by

minimizing the number of times the command byte

needs to be sent. The command address or the font

pointer address stored in the MAX6955 generally incre-

ments after each data byte is written or read (Table 6).

To utilize the autoincrement read cycle feature, the mas-

ter clocks SCL after the first data byte is read, and the

MAX6955 continues sending data, incrementing the

pointer after each byte is sent. A not-acknowledge or

stop condition halts autoincrement.

Digit Type Registers

The MAX6955 uses 32 digit registers to store the char-

acters that the user wishes to display. These digit regis-

ters are implemented with two planes, P0 and P1. Each

digit is represented by 2 bytes of memory, 1 byte in

plane P0 and the other in plane P1. The digit registers

are mapped so that a digit’s data can be updated in

plane P0, plane P1, or both planes at the same time

(Table 7).

If the blink function is disabled through the Blink Enable

Bit E (Table 20) in the configuration register, then the

digit register data in plane P0 is used to multiplex the

display. The digit register data in P1 is not used. If the

blink function is enabled, then the digit register data in

both plane P0 and plane P1 are alternately used to mul-

tiplex the display. Blinking is achieved by multiplexing

the LED display using data plane P0 and plane P1 on

alternate phases of the blink clock (Table 21).

Table 6. Command Address Autoincrement Rules

COMMAND BYTE

ADDRESS RANGE

x0000000 to x0001100

x0001101

x0001111 to x1111110

x1111111

AUTOINCREMENT BEHAVIOR

Command byte address autoincrements after byte read or written.

Factory reserved; do not write this register.

Command byte address autoincrements after byte read or written.

Command byte address remains at x1111111 after byte read or written.

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