Rainbow Electronics MAX6975 - Manual (Page 14)

MAX6974/MAX6975
Commands
The MAX6974/MAX6975 have four commands used to
load all operating mode and LED output current data.
Each command is uniquely identified by two bits, C1
and C0, embedded in the serial-interface protocol
structure. The commands Load CALDAC, Load Global-
Intensity PDM, and Load Configuration each require 24
bits of data (3 bytes) for every cascaded device. The
number of bits required for the command load individual
PWM varies by device and multiplex mode of operation.
Each cascaded device can receive unique data for
CALDACs, global intensity, configuration, and individual
PWM output drivers. Generally, all cascaded devices
are operated in the same configuration mode. The data
bytes are transmitted MSB first for all commands. The
commands are communicated to all cascaded devices
by the host using the synchronous serial-interface and
protocol structure (see the
Serial Interface section for
details). The four commands and the data lengths for
each command are shown in
Table 4.
The MAX6974, operating in nonmultiplexed mode,
requires twenty-four 12-bit individual PWM data (288
bits total) and requires forty-eight 12-bit data (576 bits
total) in multiplexed operation mode. Similarly, the
MAX6975, operating in nonmultiplexed mode, requires
twenty-four 14-bit individual-intensity PWM data (336
bits total) and requires forty-eight 14-bit (672 bits total)
data in multiplexed mode. The individual PWM data are
loaded into an intermediate latch and transferred to the
actual PWM latches at subframe 0 and PWM clock 0.
The R, G, and B calibration DACs are loaded with 8-bit
data each in nonmultiplexed and multiplexed modes.
Data is updated immediately into the CALDAC latches
(see
Table 8) .
The MAX6974/MAX6975 require one data byte to set the
global-intensity PDM for all output drivers. The global-
intensity PDM data has a variable number of active bits
depending on the multiplex operating mode and, for
the MAX6975, the global-quarter setting. The number of
bits used for global-intensity control is always justified
to the LSB of the data byte, as shown in
Table 5. One
byte of data is sent three times with the global-intensity
PDM data bits justified to the LSB. Data is updated into
the PWM latches at subframe 0 and PWM clock 0 (see
Table 9) .
When using the MAX6975 5-bit global-intensity setting,
the settings range from 0 to 63 to set the global intensity
from 1 to 64 subframes ON to 64 out of 64 subframes ON.
When using the MAX6974 7-bit global-intensity setting,
the settings range from 0 to 127 to set the global inten-
sity from 1 out of 128 subframes ON to 128 out of 128
subframes ON.
24-Output PWM LED Drivers
for Message Boards
14 ______________________________________________________________________________________
CMD[1:0]
C1 C0
COMMAND DATA LENGTH PER CASCADED DEVICE
288 bits (MAX6974 nonmultiplexed)
576 bits (MAX6974 multiplexed)
336 bits (MAX6975 nonmultiplexed)
0 0 Load individual PWM
672 bits (MAX6975 multiplexed)
0 1 Load CALDAC 24 bits
1 0 Load global-intensity PDM 24 bits
1 1 Load configuration 24 bits
Table 4. Commands and Data Length
PART GLB4 MUX TOTAL BITS MSB D7 D6 D5 D4 D3 D2 D1 LSB D0
X 0 7 0 Bit[6] Bit[5] Bit[4] Bit[3] Bit[2] Bit[1] Bit[0]
MAX6974
X 1 6 0 0 Bit[5] Bit[4] Bit[3] Bit[2] Bit[1] Bit[0]
0 0 5 0 0 0 Bit[4] Bit[3] Bit[2] Bit[1] Bit[0]
0 1 4 0 0 0 0 Bit[3] Bit[2] Bit[1] Bit[0]
1 0 3 0 0 0 0 0 Bit[2] Bit[1] Bit[0]
MAX6975
1 1 2 0 0 0 0 0 0 Bit[1] Bit[0]
Table 5. Global-Intensity Data Bit Justification