PSD312 datasheet(25/85 Pages) STMICROELECTRONICS

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PSD3XX Family

12.0

Control Signals

Consult your MCU data sheet to determine which control signals your MCU generates, and

how they operate. This section is intended to show which control signals should be

connected to what pins on the PSD3XX. You will then use PSDsoft to configure the

PSD3XX, based on the combination of control signals that your MCU outputs, for example

RD, WR, and PSEN.

The PSD3XX is compatible with the following control signals:

• ALE or AS (polarity is programmable)

• WR or R/W

• RD/E or RD/E/DS (DS for non-3X1 devices only)

• BHE or PSEN

• A19/CSI

• RESET (polarity is programmable except on low voltage versions with the V suffix).

12.1 ALE or AS

Connect the ALE or AS signal from your MCU to this pin where applicable, and program

the polarity using PSDsoft. The trailing edge (when the signal goes inactive) of ALE or AS

latches the address on any pins that have an address input. If you are using a

non-multiplexed-bus MCU that does not output an ALE or AS signal, this pin can be used

for a generic input to the PAD. Note: if your data is multiplexed with address lines other

than A0-A7, connect your address pins to AD0/A0-AD15/A15, and connect your data to

Port A (and Port B where applicable), and connect the ALE/AS signal to this pin.

12.2 WR or R/W

Your MCU should output a stand-alone write signal (WR) or a multiplexed read/write signal

(R/W). In either case, the signal should be connected to this pin.

12.3 RD/E/DS (DS option not available on 3X1 devices)

Your MCU should output any one of RD, E (clock), or DS. In any case, connect the

appropriate signal to this pin.

12.4 BHE or PSEN

t If your MCU does not output either of these signals, tie this pin to Vcc

(through a series resistor), and skip to the next signal.

t If you use an 8-bit 8031 compatible MCU that outputs a separate signal when

accessing program space, such as PSEN, connect it to this pin. You would then use

PSDsoft to configure the EPROM in the PSD3XX to respond to PSEN only or PSEN

and RD. If you have an 8031 compatible MCU, refer to the “Program/Data Space and

the 8031” section for further information.

t If you are using a 16-bit MCU, connect the BHE (or similar signal) output to this pin.

BHE enables accessing of the upper byte of the data bus. See Table 6 for information

on how this signal is used in conjunction with the A0 address line.

BHE

Operation

Whole Word

Upper Byte From/To Odd Address

Lower Byte From/To Even Address

None

Table 6. Truth Table for BHE and Address Bit A0 (16-bit MCUs only)

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