192
PWM
Type
Subroutine
Invocation
PWM(channel, dutyCycle)
Parameter
Method
Type
Description
channel
ByVal
Byte
The channel to use for PWM generation.
dutyCycle
ByVal
Single or integral
The desired duty cycle.
Discussion
This subroutine begins or modifies the generation of a PWM signal on the specified channel. The
channel must have been previously prepared for PWM generation by calling OpenPWM(). PWM
generation is performed using one of the CPUs 16-bit timers, the number of which varies depending on
the ZX model. For ZX models based on the mega32, mega644 and mega644P CPUs, there is one 16-bit
timer that jointly supports two PWM channels, numbered 1 and 2. For ZX models based on the mega128
and mega1281 CPUs, there are two 16-bit timers and each jointly supports three PWM channels,
numbered 1 through 3 and 4 through 6 respectively. For ZX models based on the mega1280 CPU, there
are four 16-bit timers and each jointly supports three PWM channels. The table below indicates the output
pin for each PWM supported channel.
Output Pins for PWM Channel Numbers
ZX Models
1
2
3
4
5
6
ZX-24, ZX-24a, ZX-24p, ZX-24n
26, D.5
27, D.4
-
-
-
-
ZX-40, ZX-40a, ZX-40p, ZX-40n
19, D.5
18, D.4
-
-
-
-
ZX-44, ZX-44a, ZX-44p, ZX-44n
14, D.5
13, D.4
-
-
-
-
ZX-24e, ZX-24ae
15, D.5
16, D.4
-
-
-
-
ZX-1281, ZX-1281n
15, B.5
16, B.6
17, B.7
5, E.3
6, E.4
7, E.5
ZX-1280, ZX-1280n
24, B.5
25, B.6
26, B.7
5, E.3
6, E.4
7, E.5
ZX-128e, ZX-1281e
23, B.5
22, B.6
21, B.7
17, E.3
16, E.4
15, E.5
ZX Models
7
8
9
10
11
12
ZX-1280, ZX-1280n
38, L.3
39, L.4
40, L.5
16, H.4
17, H.5
18, H.6
The dutyCycle parameter specifies the desired duty cycle of the generated signal, expressing the
percentage of time that the PWM signal will be at the logic 1 state. If the supplied parameter is of type
Single, the value is in percent with a resolution of 0.01%. If the supplied parameter is integral, the units
are percent, i.e., the value 100 means 100%. Specifying a Single value that is negative or any value
greater than 100 will have an undefined effect.
If this subroutine is called without a preceding call to OpenPWM() to prepare the timer, the call will have
no effect. This subroutine may be called multiple times to effect changes to the PWM signals duty cycle
while the signal is being generated. The change in duty cycle is synchronized so that it takes effect at the
beginning of the next PWM pulse.
Example
Call OpenPWM(2, 50.0, zxFastPWM) ' prepare for 50Hz Fast PWM using channel 2
Call PWM(2, 7.5) ' generate PWM with 7.5% duty cycle (1.5mS)
Call PWM(2, 6.25) ' generate PWM with 6.25% duty cycle (1.25mS)