LM8322 datasheet(18/42 Pages) NSC

18 / 42 page

14.0 PWM Output Generation

Three pulse-width modulated (PWM) outputs are provided

with advanced capabilities for ramp-up and ramp-down of the

PWM duty cycle and execution of simple to complex com-

mand sequences. These capabilities are supported by three

independent

script-execution

engines

capable

au-

tonomous operation after setup and launch by the host.

Figure 12 shows the architecture of a script-execution engine.

30013612

FIGURE 12. PWM Script Execution Engine

The host has three commands for interfacing to the script ex-

ecution engine. The following commands are always associ-

ated with one particular PWM channel:

•

PWM_WRITE — load one word into the script command

file at a specified address.

•

PWM_START — start execution of the script.

•

PWM_STOP — stop execution of the script.

Please note: The PWM_STOP command might not take im-

mediate effect if the current command being executed is a

command with long execution time. If a PWM_STOP com-

mand is sent when the PWM engine is running a long RAMP

command, the PWM will only stop after the RAMP is com-

pleted.

The script commands have their own fixed-length 16-bit for-

mat and encoding unrelated to the variable-length, byte-

based format used for host commands. A script command is

sent by the host to the LM8322 as a parameter to the

PWM_WRITE

command.

Another

parameter

the

PWM_WRITE command specifies an address in the script

command file for receiving the command.

14.1 COMMAND QUEUE

After the host issues a PWM_START command, script com-

mands are read from the script command file into a command

queue which consists of a command file output register, com-

mand buffer, and active command register. This allows one

command to be active while another command is queued in

the command buffer, which allows seamless back-to-back

command execution.

A command loaded into the command file output register is

synchronized to the 32.768 kHz clock and stored in the com-

mand buffer. If no command is currently active, the command

passes through to the active command register. In this case,

another command can be read from the script command file,

which is queued in the command buffer. On completion of the

currently active command, the contents of the command

buffer are transferred to the active command register, and the

command buffer may then receive a new command.

The host does not have direct access to any of the registers

in the command queue. The operations which read script

commands from the script command file occur automatically

after the host issues the PWM_START command.

Script execution stops when the host sends a PWM_STOP

command or when the script engine executes an END com-

mand with the Reset bit set to 1. Executing an END command

with the Reset bit set to “1” or the reception of a PWM_STOP

command asserts IRQ to the host.

14.2 PWM TIMER OPERATION

The timers implement a fixed 256-cycle period with a pro-

grammable duty cycle and programmable ramp-up/ramp-

down of the duty cycle. Figure 13 shows the architecture of a

PWM timer.

LM8322 Datasheet(PDF) 18 Page - National Semiconductor (TI)

LM8322 Datasheet(HTML) 18 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

Datasheet Download

Link URL