ZPSD301 datasheet(24/85 Pages) STMICROELECTRONICS

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PSD3XX Family

11.

PSD Memory

The following sections explain the various memory blocks and memory options within the

PSD3XX.

11.1 EPROM

For all of the PSD3XX devices, the EPROM is built using Zero-power technology. This

means that the EPROM powers up only when the address changes. It consumes power for

the necessary time to latch data on its outputs. After this, it powers down and remains in

Standby Mode until the next address change. This happens automatically, and the designer

has to do nothing special.

The EPROM is divided into eight equal-sized banks. Each bank can be placed in any

address location by programming the PAD. Bank0-Bank7 are selected by PAD A outputs

ES0-ES7, respectively. There is one product term for each bank select (ESi).

Refer to Table 1 to see the size of the EPROM for each PSD device.

11.2 SRAM (Optional)

Like the EPROM, the optional SRAM in the PSD3XX devices is built using Zero-power

technology.

All PSD3XX parts which do not have an R suffix contain 2 Kbytes of SRAM (Table 1). The

SRAM is selected by the RS0 output of the PAD. There is one product term dedicated to

RS0.

If your design requires a SRAM larger than 2K x 8, then use one of the RAMless

(R versions) of the 3XX devices with an external SRAM. The external SRAM can be

addressed trhough Port A and all require logic will be taken care of by the PSD3XXR.

11.3 Page Register (Optional)

All PSD3XX parts, except 3X1devices, have a four-bit page register. Thus the effective

address space of your MCU can be enlarged by a factor of 16. Each bit of the Page

space (at offset 18h); see Table 5. The Page Register is connected to the lowest nibble of

the data bus (D3-D0). The outputs of the Page Register, P3-P0, are connected to PAD A,

and therefor can be used in any chip select (internal or external) equations. The contents of

the page register are reset to zero at power-up and after any chip-level reset.

11.4 Programming and Erasure

Programming the device can be done using the following methods:

•ST’s main programmer—PSDpro—which is accessible through a parallel port.

• ST’s programmer used specifically with the PSD3XX—PEP300.

•ST’s discontinued programmer—Magic Pro.

• A 3rd party programmer, such as Data I/O.

Information for programming the device is available directly from ST. Please contact your

local sales representative. Also, check our web site (www.st.com/psm) for information related

to 3rd party programmers.

Upon delivery from ST or after each erasure (using windowed part), the PSD3XX device

has all bits in PAD and EPROM in the HI state (logic 1). The configuration bits are in the LO

state (logic 0).

To clear all locations of their programmed contents (assuming you have a windowed

version), expose the windowed device to an Ultra-Violet (UV) light source. A dosage of

30 W second/cm2 is required for PSD3XX devices, and 40 W second/cm2 for low-voltage

(V suffix) devices. This dosage can be obtained with exposure to a wavelength of 2537 Å

and intensity of 12000 µW/cm2 for 40 to 45 minutes for the PSD3XX and 55 to 60 minutes

for the low-voltage (V suffix) devices. The device should be approximately 1 inch (2.54 cm)

from the source, and all filters should be removed from the UV light source prior to erasure.

The PSD3XX devices will erase with light sources having wavelengths shorter than 4000 Å.

However, the erasure times will be much longer than when using the recommended 2537 Å

wavelength. Note: exposure to sunlight will eventually erase the device. If used in such an

environment, the package window should be covered with an opaque substance.

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