
PSD3XX Famly
2-13
Function
PADA and PADB Inputs
In CSI mode (when high), PAD deselects all of its outputs and enters a 
power-down mode (see Tables 12 and 13). In A19 mode, it is another 
input to the PAD.
These are general purpose inputs from Port C. See Figure 3, Note 6.
These are address inputs.
These are page number inputs (for the PSD302/312/303/313 only).
This is the read pulse or enable strobe input. (Note 10)
This is the write pulse or R/W select signal.
This is the ALE input to the chip.
This deselects all outputs from the PAD; it can not be used in product 
term equations. See Tables 10 and 11 and Figure 11.
A19/CSI
A16–A18
A11–A15
P0–P3
RD/E/DS
WR or R/W
ALE
RESET
PADA Outputs
These are internal chip-selects to the 8 EPROM banks. Each bank can
be located on any boundary that is a function of one product term of the 
PAD address inputs.
This is an internal chip-select to the SRAM. Its base address location is
a function of one term of the PAD address inputs. (Not available on 
PSD3XXR versions).
This internal chip-select selects the I/O ports. It can be placed on any 
boundary that is a function of one product term of the PAD inputs. See 
Tables 6 and 7.
This internal chip-select, when Port A is configured as a low-order 
address/data bus in the track mode (CPAF2 = 1), controls the input 
direction of Port A. CSADIN is gated externally to the PAD by the 
internal read signal. When CSADIN and a read operation are active, data
presented on Port A flows out of AD0/A0–AD7/A7. This chip-select can
be placed on any boundary that is a function of one product term of the 
PAD inputs. See Figure 5.
This internal chip-select, when Port A is configured as a low-order 
address/data bus in track mode (CPAF2 = 1), controls the output
direction of Port A. CSADOUT1 is gated externally to the PAD by the ALE 
signal. When CSADOUT1 and the ALE signal are active, the address 
presented on AD0/A0–AD7/A7 flows out of Port A. This chip-select can 
be placed on any boundary that is a function of one product term of the 
PAD inputs. See Figure 5.
This internal chip-select, when Port A is configured as a low-order 
address/data bus in the track mode (CPAF2 = 1), controls the output 
direction of Port A. CSADOUT2 must include the write-cycle control 
signals as part of its product term. When CSADOUT2  is active, the data 
presented on AD0/A0–AD7/A7 flows out of Port A. This chip-select can
be placed on any boundary that is a function of one product term of the 
PAD inputs. See Figure 5.
ES0–ES7
RS0
CSIOPORT
CSADIN
CSADOUT1
CSADOUT2
PAD B Outputs
CS0–CS3
These chip-select outputs can be routed through Port B. Each of them is
a function of up to four product terms of the PAD inputs.
These chip-select outputs can be routed through Port B. Each of them is
a function of up to two product terms of the PAD inputs.
These chip-select outputs can be routed through Port C. See Figure 3, 
Note 6. Each of them is a function of one product term of the PAD inputs.
CS4–CS7
CS8–CS10
Table 3.
PSD3XX PADA
and PADB
Functions