PSD4235G2V-10U STMICROELECTRONICS [STMicroelectronics], PSD4235G2V-10U Datasheet - Page 26

• Manufacturer Part Number: PSD4235G2V-10U
• Description: Flash In-System Programmable (ISP) Peripherals for 16-bit MCUs
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

PSD4256G6V
Primary Flash Memory and Secondary Flash memory Description
The primary Flash memory is divided evenly into 8
sectors. The secondary Flash memory is divided
into 4 sectors of different size. Each sector of ei-
ther memory block can be separately protected
from Program and Erase cycles.
Flash memory may be erased on a sector-by-sec-
tor basis, and programmed word-by-word. Flash
sector erasure may be suspended while data is
read from other sectors of the block and then re-
sumed after reading.
During a Program or Erase cycle in Flash memory,
the status can be output on the Ready/Busy pin
(PE4). This pin is set up using PSDsoft.
Memory Block Select Signals
The DPLD generates the Select signals for all the
internal memory blocks (see the section entitled
“PLDs”, on page 38). Each of the sectors of the pri-
mary Flash memory has a Select signal (FS0-
FS15) which can contain up to three product
terms. Each of the sectors of the secondary Flash
memory
CSBOOT3) which can contain up to three product
terms. Having three product terms for each Select
signal allows a given sector to be mapped in differ-
ent areas of system memory. When using a MCU
with
(80C51XA), these flexible Select signals allow dy-
namic re-mapping of sectors from one memory
space to the other before and after IAP. The
SRAM block has a single Select signal (RS0).
Ready/Busy (PE4)
This signal can be used to output the Ready/Busy
status of the PSD. The output is a '0' (Busy) when
26/100
This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to change without notice.
separate
has
a
Program
Select
signal
and
Data
(CSBOOT0-
space
a Flash memory block is being written to, or when
a Flash memory block is being erased. The output
is a '1' (Ready) when no WRITE or Erase cycle is
in progress.
Memory Operation
The primary Flash memory and secondary Flash
memory are addressed through the MCU Bus In-
terface. The MCU can access these memories in
one of two ways:
Typically, the MCU can read Flash memory using
READ operations, just as it would read a ROM de-
vice. However, Flash memory can only be erased
and programmed using specific instructions. For
example, the MCU cannot write a single byte di-
rectly to Flash memory as one would write a byte
to RAM. To program a word into Flash memory,
the MCU must execute a Program instruction, then
test the status of the Programming event. This sta-
tus test is achieved by a READ operation or polling
Ready/Busy (PE4).
Flash memory can also be read by using special
instructions to retrieve particular Flash device in-
formation (sector protect status and ID).
The MCU can execute a typical bus WRITE or
READ operation just as it would if accessing a
RAM or ROM device using standard bus cycles.
The MCU can execute a specific instruction that
consists of several WRITE and READ
operations. This involves writing specific data
patterns to special addresses within the Flash
memory to invoke an embedded algorithm.
These instructions are summarized in Table 29,
page 27.