MAX6955(2002) 데이터 시트보기 (PDF) - Maxim Integrated

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MAX6955
(Rev.:2002)

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

Maxim Integrated 

2-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

Table 5. MAX6955 Address Map

PIN CONNECTION

DEVICE ADDRESS

AD1

AD0 A6 A5 A4 A3 A2 A1 A0

GND

GND 1 1 0 0 0 0 0

GND

V+

1100001

GND

SDA 1 1 0 0 0 1 0

GND

SCL 1 1 0 0 0 1 1

V+

GND 1 1 0 0 1 0 0

V+

V+

1100101

V+

SDA 1 1 0 0 1 1 0

V+

SCL 1 1 0 0 1 1 1

SDA

GND 1 1 0 1 0 0 0

SDA

V+

1101001

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

Message Format for Reading

The MAX6955 is read using the MAX6955’s internally

stored command byte as address pointer, the same

way the stored command byte is used as address

pointer for a write. The pointer generally autoincre-

ments after each data byte is read using the same rules

as for a write (Table 6). Thus, a read is initiated by first

configuring the MAX6955’s command byte by perform-

ing a write (Figure 7). The master can now read n con-

secutive bytes from the MAX6955, with the first data

byte being read from the register addressed by the ini-

tialized command byte (Figure 9). When performing

read-after-write verification, reset the command byte’s

address because the stored byte address generally is

autoincremented after the write (Table 6).

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).

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).

The data in the digit registers does not control the digit

segments directly for 14- and 16-segment displays.

Instead, the register data is used to address a charac-

ter generator that stores the data for the 14- and 16-

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.

10 ______________________________________________________________________________________

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