Rainbow Electronics AT89S53 - Manual (Page 19)

AT89S53
19
Programming the Flash
Atmel’s AT89S53 Flash Microcontroller offers 12K bytes of
in-system reprogrammable Flash Code memory.
The AT89S53 is normally shipped with the on-chip Flash
Code memory array in the erased state (i.e. contents =
FFH) and ready to be programmed. This device supports a
High-Voltage (12V) Parallel programming mode and a Low-
Voltage (5V) Serial programming mode. The serial pro-
gramming mode provides a convenient way to download
the AT89S53 inside the user’s system. The parallel pro-
gramming mode is compatible with conventional third party
Flash or EPROM programmers.
The Code memory array occupies one contiguous address
space from 0000H to 2FFFH.
The Code array on the AT89S53 is programmed byte-by-
byte in either programming mode. An auto-erase cycle is
provided with the self-timed programming operation in the
serial programming mode. There is no need to perform the
Chip Erase operation to reprogram any memory location in
the serial programming mode unless any of the lock bits
have been programmed.
In the parallel programming mode, there is no auto-erase
cycle. To reprogram any non-blank byte, the user needs to
use the Chip Erase operation first to erase the entire Code
memory array.
Parallel Programming Algorithm: To program and verify
the AT89S53 in the parallel programming mode, the follow-
ing sequence is recommended:
1. Power-up sequence:
Apply power between V
CC
and GND pins.
Set RST pin to “H”.
Apply a 3 MHz to 24 MHz clock to XTAL1 pin and wait
for at least 10 milliseconds.
2. Set PSEN pin to “L”
ALE pin to “H”
EA pin to “H” and all other pins to “H”.
3. Apply the appropriate combination of “H” or “L” logic
levels to pins P2.6, P2.7, P3.6, P3.7 to select one of
the programming operations shown in the Flash
Programming Modes table.
4. Apply the desired byte address to pins P1.0 to P1.7
and P2.0 to P2.5.
Apply data to pins P0.0 to P0.7 for Write Code
operation.
5. Raise EA/V
PP
to 12V to enable Flash programming,
erase or verification.
6. Pulse ALE/PROG once to program a byte in the
Code memory array, or the lock bits. The byte-write
cycle is self-timed and typically takes 1.5 ms.
7. To verify the byte just programmed, bring pin P2.7
to “L” and read the programmed data at pins P0.0 to
P0.7.
8. Repeat steps 3 through 7 changing the address and
data for the entire 12K-byte array or until the end of
the object file is reached.
9. Power-off sequence:
Set XTAL1 to “L”.
Set RST and EA pins to “L”.
Turn V
CC
power off.
Data Polling: The AT89S53 features DATA Polling to indi-
cate the end of a write cycle. During a write cycle in the
parallel or serial programming mode, an attempted read of
the last byte written will result in the complement of the writ-
ten datum on P0.7 (parallel mode), and on the MSB of the
serial output byte on MISO (serial mode). Once the write
cycle has been completed, true data are valid on all out-
puts, and the next cycle may begin. DATA Polling may
begin any time after a write cycle has been initiated.
Ready/Busy: The progress of byte programming in the
parallel programming mode can also be monitored by the
RDY/BSY output signal. Pin P3.4 is pulled Low after ALE
goes High during programming to indicate BUSY. P3.4 is
pulled High again when programming is done to indicate
READY.
Program Verify: If lock bits LB1 and LB2 have not been
programmed, the programmed Code can be read back via
the address and data lines for verification. The state of the
lock bits can also be verified directly in the parallel pro-
gramming mode. In the serial programming mode, the state
of the lock bits can only be verified indirectly by observing
that the lock bit features are enabled.
Chip Erase: In the parallel programming mode, chip erase
is initiated by using the proper combination of control sig-
nals and by holding ALE/PROG low for 10 ms. The Code
array is written with all “1”s in the Chip Erase operation.
In the serial programming mode, a chip erase operation is
initiated by issuing the Chip Erase instruction. In this mode,
chip erase is self-timed and takes about 16 ms.
During chip erase, a serial read from any address location
will return 00H at the data outputs.
Serial Programming Fuse: A programmable fuse is avail-
able to disable Serial Programming if the user needs
maximum system security. The Serial Programming Fuse
can only be programmed or erased in the Parallel Program-
ming Mode.
The AT89S53 is shipped with the Serial Programming
Mode enabled.