Rainbow Electronics MAX7315 - Manual (Page 16)

MAX7315
Reading a blink phase register reads the value stored
in the register, not the actual port condition. The port
output itself may or may not be at a valid logic level,
depending on the external load connected.
The 9th output, O8, is controlled through 2 bits in the
configuration register, which provide the same static or
blink control as the other 8 output ports.
PWM Intensity Control
The MAX7315 includes an internal oscillator, nominally
32kHz, to generate PWM timing for LED intensity con-
trol or other applications such as PWM trim DACs. PWM
can be disabled entirely for all the outputs. In this case,
all outputs are static and the MAX7315 operating cur-
rent is lowest because the internal PWM oscillator is
turned off.
The MAX7315 can be configured to provide any combi-
nation of PWM outputs and glitch-free logic outputs.
Each PWM output has an individual 4-bit intensity con-
trol (Table 14). When all outputs are to be used with the
same PWM setting, the outputs can be controlled
together instead using the global intensity control
(Table 13). Table 10 shows how to set up the MAX7315
to suit a particular application.
PWM Timing
The PWM control uses a 240-step PWM period, divided
into 15 master intensity timeslots. Each master intensity
timeslot is divided further into 16 PWM cycles (Figure 11).
The master intensity operates as a gate, allowing the indi-
vidual output settings to be enabled from 1 to 15 timeslots
per PWM period (Figures 12, 13, 14) (Table 13).
Each output’s individual 4-bit intensity control only
operates during the number of timeslots gated by the
master intensity. The individual controls provide 16
intensity settings from 1/16 through 16/16 (Table 14).
Figures 15, 16, and 17 show examples of individual
intensity control settings. The highest value an individ-
ual or global setting can be set to is 16/16. This setting
forces the output to ignore the master control, and fol-
low the logic level set by the appropriate blink phase
register bit. The output becomes a glitch-free static out-
put with no PWM.
Using PWM Intensity Controls with Blink Disabled
When blink is disabled (Table 7), the blink phase 0 reg-
ister specifies each output’s logic level during the PWM
on-time (Table 8). The effect of setting an output’s blink
phase 0 register bit to 0 or 1 is shown in Table 11. With
its output bit set to zero, an LED can be controlled with
16 intensity settings from 1/16th duty through fully on,
but cannot be turned fully off using the PWM intensity
control. With its output bit set to 1, an LED can be con-
trolled with 16 intensity settings from fully off through
15/16th duty.
8-Port I/O Expander with LED Intensity
Control and Interrupt
16 ______________________________________________________________________________________
Table 5. Ports Configuration Register
REGISTER DATA
REGISTER R/ W
ADDRESS
CODE
(HEX)
D7 D6 D5 D4 D3 D2 D1 D0
Ports configuration
(1 = input, 0 = output)
0
Read-back ports configuration 1
0x03 OP7 OP6 OP5 OP4 OP3 OP2 OP1 OP0
Table 6. Input Ports Register
REGISTER DATA
REGISTER R/ W
ADDRESS
CODE
(HEX)
D7 D6 D5 D4 D3 D2 D1 D0
Read input ports 1 0x00 IP7 IP6 IP5 IP4 IP3 IP2 IP1 IP0
Table 7. Blink Controls
BLINK
ENABLE
FLAG E
BLINK
FLIP
FLAG B
BLINK
FUNCTION
OUTPUT
REGISTERS
USED
0 X Disabled
Blink phase 0
register
0
Blink phase 0
register
1
1
Enabled
Blink phase 1
register