Datasheet

Register Control of I/O Ports and LEDs
Across Multiple Drivers
The MAX6957 offers 20 or 28 I/O ports, depending
on package choice. These can be applied to a variety
of combinations of different display types, for exam-
ple: seven, 7-segment digits (Figure 2). This example
requires two MAX6957s, with one digit being driven by
both devices, half by one MAX6957, half by the other
(digit 4 in this example). The two drivers are static,
and therefore do not need to be synchronized. The
MAX6957 sees CA digits as multiple discrete LEDs. To
simplify access to displays that overlap two MAX6957s,
the MAX6957 provides four virtual ports P0 through P3.
To update an overlapping digit, send the same code
twice as an eight-port write, once to P28 through P35 of
the first driver, and again to P0 through P7 of the sec-
ond driver. The first driver ignores the last 4 bits and the
second driver ignores the first 4 bits.
Two addressing methods are available. Any single
port (bit) can be written (set/cleared) at once; or, any
sequence of eight ports can be written (set/cleared) in
any combination at once. There are no boundaries; it is
equally acceptable to write P0 through P7, P1 through
P8, or P31 through P38 (P32 through P38 are nonexis-
tent, so the instructions to these bits are ignored).
Using 8-bit control, a seven-segment digit with a decimal
point can be updated in a single byte-write, a 14-segment
digit with DP can be updated in two byte-writes, and
16-segment digits with DP can be updated in two byte-
writes plus a bit write. Also, discrete LEDs and GPIO port
bits can be lit and controlled individually without affecting
other ports.
Note: The logic is inverted between the two output modes; a high makes the output go low in LED segment driver mode (0x00) to
turn that segment on; in GPIO output mode (0x01), a high makes the output go high.
Table 2. Port Configuration Matrix
Table 1. Port Configuration Map
MODE FUNCTION
PORT
REGISTER
(0x20–0x5F)
(0xA0–0xDF)
PIN BEHAVIOR
ADDRESS
CODE (HEX)
PORT
CONFIGURATION
BIT PAIR
UPPER LOWER
Output LED Segment Driver
Register bit = 0 High impedance
0x09 to 0x0F 0 0
Register bit = 1
Open-drain current sink, with sink
current (up to 24mA) determined
by the appropriate current register
Output GPIO Output Register bit = 0
Active-low logic output
0x09 to 0x0F 0 1
Active-high logic output
Input
GPIO Input
Without Pullup
Register bit =
input logic level
Schmitt logic input 0x09 to 0x0F 1 0
Input GPIO Input with Pullup Schmitt logic input with pullup 0x09 to 0x0F 1 1
REGISTER
ADDRESS
CODE (HEX)
REGISTER DATA
D7 D6 D5 D4 D3 D2 D1 D0
Port Configuration for P7, P6, P5, P4 0x09 P7 P6 P5 P4
Port Configuration for P11, P10, P9, P8 0x0A P11 P10 P9 P8
Port Configuration for P15, P14, P13, P12 0x0B P15 P14 P13 P12
Port Configuration for P19, P18, P17, P16 0x0C P19 P18 P17 P16
Port Configuration for P23, P22, P21, P20 0x0D P23 P22 P21 P20
Port Configuration for P27, P26, P25, P24 0x0E P27 P26 P25 P24
Port Configuration for P31, P30, P29, P28 0x0F P31 P30 P29 P28
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MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander