Datasheet
AT89S53
4-236
Instruction Set
Notes: 1. DATA polling is used to indicate the end of a write cycle which typically takes less than 2.5 ms at 5V.
2. “x” = don’t care.
Instruction Input Format Operation
Byte 1 Byte 2 Byte 3
Programming Enable 1010 1100 0101 0011 xxxx xxxx Enable serial programming interface after RST goes high.
Chip Erase 1010 1100 xxxx x100 xxxx xxxx Chip erase the 12K memory array.
Read Code Memory low addr xxxx xxxx Read data from Code memory array at the selected address.
The 6 MSBs of the first byte are the high order address bits.
The low order address bits are in the second byte. Data are
available at pin MISO during the third byte.
Write Code Memory low addr data in Write data to Code memory location at selected address. The
address bits are the 6 MSBs of the first byte together with the
second byte.
Write Lock Bits 1010 1100 xxxx xxxx Write lock bits.
Set LB1, LB2 or LB3 = “0” to program lock bits.
LB1
LB2
LB3
A12
A11
A10
A9
A8
A13
01
A12
A11
A10
A9
A8
A13
10
xx111
Serial Programming Algorithm
To program and verify the AT89S53 in the serial program-
ming mode, the following sequence is recommended:
1. Power-up sequence:
Apply power between V
CC
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.
2. Enable serial programming by sending the Program-
ming Enable serial instruction to pin MOSI/P1.5. The
frequency of the shift clock supplied at pin SCK/P1.7
needs to be less than the CPU clock at XTAL1 divided
by 40.
3. 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 typically takes
less than 2.5 ms at 5V.
4. 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.
5. 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”.
Tur n 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: