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.
Serial Programming Algorithm
To program and verify the AT89S53 in the serial program-
ming mode, the following sequence is recommended:
5. At the end of a programming session, RST can be set
low to commence normal operation.
1. Power-up sequence:
Apply power between VCC and GND pins.
Set RST pin to “H”.
Power-off sequence (if needed):
Set XTAL1 to “L” (if a crystal is not used).
Set RST to “L”.
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.
Tur n VCC power off.
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.
Serial Programming Instruction
The Instruction Set for Serial Programming follows a 3-byte
protocol and is shown in the following table:
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.
Instruction Set
Instruction
Input Format
Byte 2
Operation
Byte 1
Byte 3
Programming Enable
Chip Erase
1010 1100
1010 1100
0101 0011
xxxx x100
low addr
xxxx xxxx
xxxx xxxx
xxxx xxxx
Enable serial programming interface after RST goes high.
Chip erase the 12K memory array.
Read Code Memory
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.
01
Write Code Memory
Write Lock Bits
low addr
x x111
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.
10
1010 1100
xxxx xxxx
Write lock bits.
Set LB1, LB2 or LB3 = “0” to program lock bits.
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.
AT89S53
4-236
ATMEL [ ATMEL ]
