p87lpc778 NXP Semiconductors, p87lpc778 Datasheet - Page 21

• Manufacturer Part Number: p87lpc778
• Description: Cmos Single-chip 8-bit 80c51 Microcontroller 128-byte Data Ram, 8 Kb Otp
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 12378
Product data
When the counter reaches underflow it is reloaded with a user selectable value. This
mechanism allows the user to set the PWM frequency at any integer sub-multiple of
the microcontroller clock frequency. The repetition frequency of the PWM is given by:
Where CNSW is contained in SFRs CNSW0 and CNSW1 as a 10-bit value,
described in the following tables.
The word ‘Shadow’ refers to the fact that writes are not into the register that controls
the counter; rather they are into a holding register.
As described below the transfer of data from this holding register, into the register
which contains the actual reload value, is controlled by the user’s program, by setting
the XFER bit and waiting till the next underflow of the counter.
Table 11:
Reset value: FFH
Table 12:
Reset value: FFH
f
Bit
Symbol
Bit
Symbol
PWM
=
------------------------------ -
CNSW
CNSW7
CNSW0 - Counter shadow register 0 (address 0D1H) bit allocation
CNSW1 - Counter shadow register 1 (address 0D2H) bit allocation
Unused
f
CPWM
7
7
+
Rev. 01 — 31 March 2004
1
CNSW6 CNSW5 CNSW4
Unused
6
6
Unused
5
5
Unused
4
4
CMOS single-chip 8-bit microcontroller
CNSW3
Unused
3
3
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
CNSW2 CNSW1 CNSW0
Unused CNSW9 CNSW8
P87LPC778
2
2
1
1
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0
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