Rainbow Electronics T89C51RD2 - Manual (Page 58)

Rev. F - 15 February, 2001 58
T89C51RD2
8.7. In-System Programming (ISP)
The In-System Programming (ISP) is performed without removing the microcontroller from the system. The In-
System Programming (ISP) facility consists of a series of internal hardware resources coupled with internal firmware
to facilitate remote programming of the T89C51RD2 through the serial port. This firmware is embedded within
each T89C51RD2 device going out of factory.
The ATMEL Wireless and Microcontrollers In-System Programming (ISP) facility has made in-circuit programming
in an embedded application possible with a minimum of additional expense in components and circuit board area.
The ISP function uses four pins: TxD, RxD, V
SS
, V
CC
. Only a small connector needs to be available to interface
the application to an external circuit in order to use this feature. Application schematic can found be in the
demonstration and ISP board user manual.
Using the In-System Programming (ISP)
The ISP feature allows a wide range of baud rates in the user application. It is also adaptable to a wide range of
oscillator frequencies. This is accomplished by measuring the bit-time of a single bit in a received character. This
information is then used to program the baud rate in terms of timer counts based on the oscillator frequency. The
ISP feature requires that an initial character (an uppercase U) be sent to the T89C51RD2 to establish the baud
rate. The ISP firmware provides auto-echo of received characters.
Once baud rate initialization has been performed, the ISP firmware will only accept Intel Hex-type records. Intel
Hex records consist of ASCII characters used to represent hexadecimal values and are summarized below:
:NNAAAARRDD..DDCC
In the Intel Hex record, the “NN” represents the number of data bytes in the record. The T89C51RD2 will accept
up to 16 (10h) data bytes. The “AAAA” string represents the address of the first byte in the record. If there are
zero bytes in the record, this field is often set to ‘‘0000’’. The “RR” string indicates the record type. A record
type of “00” is a data record. A record type of “01” indicates the end-of-file mark. In this application, additional
record types will be added to indicate either commands or data for the ISP facility. The “DD” string represents
the data bytes. The maximum number of data bytes in a record is limited to 16 (decimal). The “CC” string
represents the checksum byte. ISP commands are summarized in Table 32.
As a record is received by the T89C51RD2, the information in the record is stored internally and a checksum
calculation is performed and compared to ‘‘CC’’.
The operation indicated by the record type is not performed until the entire record has been received. Should an
error occur in the checksum, the T89C51RD2 will send an “X” out the serial port indicating a checksum error. If
the checksum calculation is found to match the checksum in the record, then the command will be executed. In
most cases, successful reception of the record will be indicated by transmitting a “.” character out the serial port
(displaying the contents of the internal program memory is an exception).
In the case of a Data Record (record type ‘‘00’’), an additional check is made. A “.” character will NOT be sent
unless the record checksum matched the calculated checksum and all of the bytes in the record were successfully
programmed. For a data record, an “X” indicates that the checksum failed to match, and an “R” character indicates
that one of the bytes did not properly program.
ATMEL Wireless and Microcontrollers_ISP, a software utility to implement ISP programming with a PC, is
available from ATMEL Wireless and Microcontrollers. Please visit our web site http://www.atmel-wm.com.