PCF8811USLASH2DASLASH1 datasheet(56/73 Pages) PHILIPS

56 / 73 page

2004 May 17

Philips Semiconductors

Product speciﬁcation

× 128 pixels matrix LCD driver

PCF8811

22.2

Temperature coefﬁcient selection

The second feature is an OTP factory default setting for

the temperature coefficient selection (MMTC) in the basic

command set. This 3-bit value will be loaded from OTP

after leaving the power-save mode or by the refresh

command. The idea of this feature is to provide, in the

basic command set, the complete set of temperature

coefficients without an additional command. In the

extended command set the temperature coefficient can be

programmed as given in Table 16.

22.3

Seal bit

The module maker programming is performed in a special

mode: the calibration mode (CALMM). This mode is

entered via a special interface command, CALMM.

To prevent wrongful programming, a seal bit has been

implemented which prevents the device from entering the

calibration mode. This seal bit, once programmed, can not

be reversed, thus further changes in programmed values

are not possible.

Applying the programming voltages when not in CALMM

mode will have no effect on the programmed values.

Table 23 Seal bit deﬁnition

22.4

OTP architecture

The OTP circuitry in the PCF8811 contains 9 bits of data:

5 for VLCD calibration (MMVOPCAL), 3 for the temperature

coefficient default setting in the basic command set MMTC

and 1 seal bit. The circuitry for 1-bit is called an OTP slice.

Each OTP slice consists of 2 main parts: the OTP cell (a

non-volatile memory cell) and the shift register cell (a

flip-flop). The OTP cells are only accessible through their

shift register cells: on the one hand both reading from and

writing to the OTP cells is performed with the shift register

cells, on the other hand only the shift register cells are

visible to the rest of the circuit. The basic OTP architecture

is shown in Fig.48.

This OTP architecture allows the following operations:

1. Reading data from the OTP cells. The content of the

non-volatile OTP cells is transferred to the shift

operation.

2. Writing data to the OTP cells. First, all 9 bits of data are

shifted into the shift register via the interface. The

content of the shift register is then transferred to the

OTP cells (there are some limitations related to storing

data in these cells; see Section 22.7).

3. Checking calibration without writing to the OTP cells.

Shifting data into the shift register allows the effects on

the VLCD voltage to be observed.

The reading of data from the OTP cells is initiated by

either:

• Exit from power-save mode

• The ‘Refresh’ command (power control).

It should be noted that in both cases the reading operation

needs up to 5 ms to complete.

The shifting of data into the shift register is performed in

the special mode CALMM. In the PCF8811 the CALMM

mode is entered by the CALMM command. Once in the

CALMM mode the data is shifted into the shift register via

the interface at the rate of 1-bit per command. After

transmitting the last (9th) bit and exiting the CALMM mode,

the serial interface will return to the normal mode and all

other commands can be sent. Care should be taken that

9 bits of data (or a multiple of 9) are always transferred

before exiting the CALMM mode, otherwise the bits will be

in the wrong positions.

In the shift register the value of the seal bit is, like the

others, always zero at reset. To ensure that the security

feature works correctly, the CALMM command is disabled

until a refresh has been performed. Once the refresh is

completed, the seal bit value in the shift register will be

valid and permission to enter the CALMM mode can thus

be determined.

The 9 bits are shifted into the shift register in a predefined

order: first 5 bits of MMVOPCAL[4:0], 3 bits for MMTC[2:0]

and lastly the seal bit. The MSB is always first, thus the first

bit shifted is MMVOPCAL[4] and the two last bits are

MMTC[0] and the seal bit.

SEAL BIT

ACTION

possible to enter calibration mode

calibration mode disabled

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