The PSD835G2 device offers two methods to program PSD Flash memory while the PSD
is soldered to a circuit board.
t In-System Programming (ISP) via JTAG
An IEEE 1149.1 compliant JTAG-ISP interface is included on the PSD enabling the
entire device (both flash memories, the PLD, and all configuration) to be rapidly
programmed while soldered to the circuit board. This requires no MCU participation,
which means the PSD can be programmed anytime, even while completely blank.
The innovative JTAG interface to flash memories is an industry first, solving key
problems faced by designers and manufacturing houses, such as:
• First time programming – How do I get firmware into the flash the very first time?
JTAG is the answer, program the PSD while blank with no MCU involvement.
• Inventory build-up of pre-programmed devices – How do I maintain an accurate
count of pre-programmed flash memory and PLD devices based on customer
demand? How many and what version? JTAG is the answer, build your hardware
with blank PSDs soldered directly to the board and then custom program just before
they are shipped to customer. No more labels on chips and no more wasted
• Expensive sockets – How do I eliminate the need for expensive and unreliable
sockets? JTAG is the answer. Solder the PSD directly to the circuit board. Program
first time and subsequent times with JTAG. No need to handle devices and bend the
t In-Application re-Programming (IAP)
Two independent flash memory arrays are included so the MCU can execute code
from one memory while erasing and programming the other. Robust product firmware
updates in the field are possible over any communication channel (CAN, Ethernet,
UART, J1850, etc) using this unique architecture. Designers are relieved of these
• Simultaneous read and write to flash memory – How can the MCU program the
same memory from which it is executing code? It cannot. The PSD allows the MCU
to operate the two flash memories concurrently, reading code from one while erasing
and programming the other during IAP.
• Complex memory mapping – How can I map these two memories efficiently?
A Programmable Decode PLD is embedded in the PSD. The concurrent PSD
memories can be mapped anywhere in MCU address space, segment by segment
with extremely high address resolution. As an option, the secondary flash memory
can be swapped out of the system memory map when IAP is complete. A built-in
page register breaks the MCU address limit.
• Separate program and data space – How can I write to flash memory while it
resides in “program” space during field firmware updates, my 80C51 won’t allow it
The flash PSD provides means to “reclassify” flash memory as “data” space during
IAP, then back to “program” space when complete.
PSDsoft – ST’s software development tool – guides you through the design
process step-by-step making it possible to complete an embedded MCU design
capable of ISP/IAP in just hours. Select your MCU and PSDsoft will take you through
the remainder of the design with point and click entry, covering...PSD selection, pin
definitions, programmable logic inputs and outputs, MCU memory map definition, ANSI C
code generation for your MCU, and merging your MCU firmware with the PSD design.
When complete, two different device programmers are supported directly from PSDsoft –
FlashLINK (JTAG) and PSDpro.
The PSD835G2 is available in an 80-pin TQFP package.
Please refer to the revision block at the end of this
document for updated information.