PCD3755AP datasheet(17/32 Pages) PHILIPS

17 / 32 page

1997 Apr 16

Philips Semiconductors

Product speciﬁcation

8-bit microcontrollers with DTMF generator,

8 kbytes OTP and 128 bytes EEPROM

PCD3755A; PCD3755E;

PCD3755F

7.5.5

ERASE PAGE

The EEPROM flags are set as described in Section 7.5.1.

The corresponding page bytes are erased.

The last instruction also starts Timer 2. Erasure takes

5 ms. A single-byte erase is simply a special case of ‘erase

page’.

Note that ADDR does not auto-increment after an erase

cycle.

Table 22 Erase page

7.6

Timer 2

Timer 2 is a 8-bit down-counter decremented at a rate of

⁄

480 × fxtal. It may be used either for EEPROM timing or as

a general purpose timer. Conflicts between the two

applications should be carefully avoided.

7.6.1

TIMER 2 FOR EEPROM TIMING

When used for EEPROM timing, Timer 2 serves to

generate the 5 ms intervals needed for erasing or writing

the EEPROM. At the decrement rate of 1

⁄480 × fxtal, the

reload value for a 5 ms interval is a function of fxtal.

Table 23 summarizes the required reload values for a

number of oscillator frequencies.

Timer 2 is started by setting bit EWP in the EPCR.

The Timer Register T2 is loaded with the reload value from

RELR. T2 decrements to zero.

For an erase/write cycle, underflow of T2 indicates the end

of the erase operation. Therefore, Timer Register T2 is

reloaded from RELR for another 5 ms interval during

which the flagged EEPROM latches are copied to the

corresponding bytes in the page addressed by ADDR.

INSTRUCTION

RESULT

MOV A, #EWP + MC3 + MC2 + MC1 ‘erase page’

control word

MOV EPCR, A

start ‘erase

page’ cycle

The second underflow of an erase/write cycle and the first

underflow of write page and erase page conclude the

corresponding EEPROM cycle. Timer 2 is stopped, T2F is

set whereas EWP and MC1 to MC3 are cleared.

Table 23 Reload values as a function of fxtal

Note

1. The reload value is (5

× 10−3 × 1⁄480 × fxtal) − 1;

fxtal in MHz.

7.6.2

TIMER 2 AS A GENERAL PURPOSE TIMER

When used for purposes other than EEPROM timing,

Timer 2 is started by setting STT2. The Timer Register T2

(see Table 26) is loaded with the reload value from RELR.

T2 decrements to zero. On underflow, T2 is reloaded from

RELR, T2F is set and T2 continues to decrement.

Timer 2 can be stopped at any time by clearing STT2.

The value of T2 is then held and can be read out. After

setting STT2 again, Timer 2 decrements from the reload

value. Alternatively, it is possible to read T2 ‘on the fly’ i.e.

while Timer 2 is operating.

fxtal

(MHz)

RELOAD VALUE(1)

(HEX)

10A

214

3.58

63E

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