PSD835G2-90U STMicroelectronics, PSD835G2-90U Datasheet - Page 48

• Manufacturer Part Number: PSD835G2-90U
• Description: IC FLASH 4MBIT 90NS 80TQFP
• Manufacturer: STMicroelectronics

Specifications of PSD835G2-90U

• Format - Memory: FLASH
• Memory Type: FLASH
• Memory Size: 4M (512K x 8)
• Speed: 90ns
• Interface: Parallel
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 80-TQFP, 80-VQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-2015

Sector Select and SRAM Select
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12.1
12.2
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Sector Select and SRAM Select
Sector Select (FS0-FS7 for primary Flash memory, CSBOOT0-CSBOOT3 for secondary
Flash memory) and SRAM Select (RS0) are all outputs of the DPLD. They are setup using
PSDsoft. The following rules apply to the equations for these signals:
1.
2.
3.
4.
5.
6.
Example
FS0 is valid when the address is in the range of 8000h to BFFFh, CSBOOT0 is valid from
8000h to 9FFFh, and RS0 is valid from 8000h to 87FFh. Any address in the range of RS0
always accesses the SRAM. Any address in the range of CSBOOT0 greater than 87FFh
(and less than 9FFFh) automatically addresses secondary Flash memory segment 0. Any
address greater than 9FFFh accesses the primary Flash memory segment 0. You can see
that half of the primary Flash memory segment 0 and one-fourth of secondary Flash
memory segment 0 cannot be accessed in this example. Also note that an equation that
defined FS1 to anywhere in the range of 8000h to BFFFh would not be valid.
Figure 8
level can overlap and has priority over any component on a lower level. Components on the
same level must not overlap. Level one has the highest priority and level 3 has the lowest.
Memory Select configuration for MCUs with separate
program and data spaces
The 80C51 and compatible family of MCUs have separate address spaces for program
memory (selected using Program Select Enable (PSEN, CNTL2)) and data memory
(selected using Read Strobe (RD, CNTL1)). Any of the memories within the PSD can reside
in either space or both spaces. This is controlled through manipulation of the VM register
that resides in the CSIOP space.
The VM register is set using PSDsoft to have an initial value. It can subsequently be
changed by the MCU so that memory mapping can be changed on-the-fly.
For example, you may wish to have SRAM and primary Flash memory in the data space at
Boot-up, and secondary Flash memory in the program space at Boot-up, and later swap the
primary and secondary Flash memories. This is easily done with the VM register by using
PSDsoft to configure it for Boot-up and having the MCU change it when desired.
Primary Flash memory and secondary Flash memory Sector Select signals must not
be larger than the physical sector size.
Any primary Flash memory sector must not be mapped in the same memory space as
another primary Flash memory sector.
A secondary Flash memory sector must not be mapped in the same memory space as
another secondary Flash memory sector.
SRAM and I/O spaces must not overlap.
A secondary Flash memory sector may overlap a primary Flash memory sector. In
case of overlap, priority is given to the secondary Flash memory sector.
SRAM and I/O spaces may overlap any other memory sector. Priority is given to the
SRAM and I/O.
shows the priority levels for all memory components. Any component on a higher
PSD835G2