Rainbow Electronics MAX6964 - Manual (Page 6)

MAX6964
Functional Overview
The MAX6964 is a general-purpose output (GPO)
peripheral that provides 17 output ports, O0–O16, con-
trolled through an I
2 C-compatible serial interface. All
outputs sink loads up to 50mA connected to external
supplies up to 7V, independent of the MAX6964’s sup-
ply voltage. The MAX6964 is rated for a ground current
of 350mA, allowing all 17 outputs to sink 20mA at the
same time.
Figure 1 shows the output structure of the
MAX6964. The outputs default to logic high (high
impedance unless external pullup resistors are used)
on power-up.
Output Control and LED Blinking
The two blink phase 0 registers set the output logic lev-
els of the 16 outputs O0–O15 (Table 6). These registers
control the port outputs if the blink function is disabled.
A duplicate pair of registers, the blink phase 1 regis-
ters, are also used if the blink function is enabled
(
Table 7 ). In blink mode, the outputs can be flipped
between using the blink phase 0 registers, and the
blink phase 1 registers using hardware control (the
BLINK input) and/or software control (the blink flip flag
in the configuration register) (
Table 4 ).
The 17th output, O16, is controlled through 2 bits in the
configuration register, which provide the same static or
blink control as the other 16 outputs (
Table 4 ).
The logic level of the BLINK input may be read back
through the blink status bit in the configuration register
(
Table 4 ). The BLINK input, therefore, may be used as
a general-purpose logic input (GPI port) if the blink
function is not required.
PWM Intensity Control
The MAX6964 includes an internal oscillator, nominally
32kHz, to generate PWM timing for LED intensity con-
trol. PWM intensity control can be enabled on an out-
put-by-output basis, allowing the MAX6964 to provide
any mix of PWM LED drives and glitch-free logic out-
puts (
Table 8 ). PWM can be disabled entirely, in which
case all outputs are static and the MAX6964 operating
current is lowest because the internal oscillator is
turned off.
PWM intensity control uses a 4-bit master control and 4
bits of individual control per output (
Tables 11 and 12 ).
The 4-bit master control provides 16 levels of overall
intensity control, which applies to all PWM-enabled out-
puts. The master control sets the maximum pulse width
from 1/15 to 15/15 of the PWM time period. The individ-
ual settings comprise a 4-bit number, further reducing
the duty cycle to be from 1/16 to 15/16 of the time win-
dow set by the master control.
For applications requiring the same PWM setting for all
output ports, a single global PWM control can be used
instead of all the individual controls to simplify the con-
trol software and provide 240 steps of intensity control
(
Tables 8 and 11 ).
17-Output LED Driver/GPO
with Intensity Control
6 _______________________________________________________________________________________
Figure 1. Simplified Schematic of I/O Ports
DATA FROM
SHIFT REGISTER
WRITE PULSE
D
C K
Q
Q
FF
OUTPUT
PORT
REGISTER
I/O PIN
Q2
GND
OUTPUT PORT
REGISTER DATA
Figure 2. 2-Wire Serial Interface Timing Details
SCL
SDA
t R t F
t BUF
START
CONDITION
STOP
CONDITION
REPEATED START CONDITION START CONDITION
t SU,STO
t HD,STA
t SU,STA
t HD,DAT
t SU,DAT
t LOW
t HIGH
t HD,STA