7
Specifications ispGDX240VA
Figure 6. Data Bus Byte Swapper
Figure 7. Four-Port Memory Interface
Control Bus
Data Bus A
Data Bus B
OEA OEB
I/OA
D0-7
D8-15 D8-15
D0-7
I/OB
XCVR
OEA OEB
I/OA I/OB
XCVR
OEA OEB
I/OA I/OB
XCVR
OEA OEB
I/OA I/OB
XCVR
Bus 4
Bus 3
Bus 2
Bus 1
Port #1
OE1
Memory
Port
OEM
SEL0
SEL1
To
Memory
Port #2
OE2
Port #3
OE3
Note: All OE and SEL lines driven by external arbiter logic (not shown).
Port #4
OE4
4-to-1
16-Bit MUX
Bidirectional
Figure 5. Address Demultiplex/Data Buffering
Control Bus
MUXed Address Data Bus
DQ
CLK
OEA OEB
I/OA I/OB
Address
Buffered
Data
To Memory/
Peripherals
XCVR
Address
Latch
Applications (Continued)
Designing with the ispGDXVA
As mentioned earlier, this architecture satisfies the PRSI
class of applications without restrictions: any I/O pin as a
single input or bidirectional can drive any other I/O pin as
output.
For the case of PDP applications, the designer does have
to take into consideration the limitations on pins that can
be used as control (MUX0, MUX1, OE, CLK) or data
(MUXA-D) inputs. The restrictions on control inputs are
not likely to cause any major design issues because the
input possibilities span 25% of the total pins.
The MUXA-D input partitioning requires that designers
consciously assign pinouts so that MUX inputs are in the
appropriate, disjoint groups. For example, since the
MUXA group includes I/O A0-39 (240 I/O device), it is not
possible to use I/O A0 and I/O A9 in the same MUX
function. As previously discussed, data path functions
will be assigned early in the design process and these
restrictions are reasonable in order to optimize speed
and cost.
User Electronic Signature
The ispGDXVA Family includes dedicated User Elec-
tronic Signature (UES) E
2
CMOS storage to allow users
to code design-specific information into the devices to
identify particular manufacturing dates, code revisions,
or the like. The UES information is accessible through
the boundary scan programming port via a specific com-
mand. This information can be read even when the
security cell is programmed.
Security
The ispGDXVA Family includes a security feature that
prevents reading the device program once set. Even
when set, it does not inhibit reading the UES or device ID
code. It can be erased only via a device bulk erase.
