AT89S53_00 datasheet(20/33 Pages) ATMEL

20 / 33 page

AT89S53

Reading the Signature Bytes: The signature bytes are

read by the same procedure as a normal verification of

locations 030H and 031H, except that P3.6 and P3.7 must

be pulled to a logic low. The values returned are as follows:

(030H) = 1EH indicates manufactured by Atmel

(031H) = 53H indicates 89S53

Programming Interface

Every code byte in the Flash array can be written, and the

entire array can be erased, by using the appropriate combi-

nation of control signals. The write operation cycle is self-

timed and once initiated, will automatically time itself to

completion.

All major programming vendors offer worldwide support for

the Atmel microcontroller series. Please contact your local

programming vendor for the appropriate software revision.

Serial Downloading

The Code memory array can be programmed using the

serial SPI bus while RST is pulled to V

CC. The serial inter-

face consists of pins SCK, MOSI (input) and MISO (output).

After RST is set high, the Programming Enable instruction

needs to be executed first before program/erase operations

can be executed.

An auto-erase cycle is built into the self-timed programming

operation (in the serial mode ONLY) and there is no need

to first execute the Chip Erase instruction unless any of the

lock bits have been programmed. The Chip Erase opera-

tion turns the content of every memory location in the Code

array into FFH.

The Code memory array has an address space of 0000H to

2FFFH.

Either an external system clock is supplied at pin XTAL1 or

a crystal needs to be connected across pins XTAL1 and

XTAL2. The maximum serial clock (SCK) frequency should

be less than 1/40 of the crystal frequency. With a 24 MHz

oscillator clock, the maximum SCK frequency is 600 kHz.

Serial Programming Algorithm

To program and verify the AT89S53 in the serial program-

ming mode, the following sequence is recommended:

Power-up sequence:

Apply power between VCC and GND pins.

Set RST pin to “H”.

If a crystal is not connected across pins XTAL1 and

XTAL2, apply a 3 MHz to 24 MHz clock to XTAL1 pin

and wait for at least 10 milliseconds.

Enable serial programming by sending the Pro-

gramming Enable serial instruction to pin

MOSI/P1.5. The frequency of the shift clock sup-

plied at pin SCK/P1.7 needs to be less than the

CPU clock at XTAL1 divided by 40.

The Code array is programmed one byte at a time

by supplying the address and data together with the

appropriate Write instruction. The selected memory

location is first automatically erased before new

data is written. The write cycle is self-timed and typ-

ically takes less than 2.5 ms at 5V.

Any memory location can be verified by using the

Read instruction which returns the content at the

selected address at serial output MISO/P1.6.

At the end of a programming session, RST can be

set low to commence normal operation.

Power-off sequence (if needed):

Set XTAL1 to “L” (if a crystal is not used).

Set RST to “L”.

Turn V

CC power off.

Serial Programming Instruction

The Instruction Set for Serial Programming follows a 3 byte

protocol and is shown in the following table.

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