I/O Software Control in Low-Power Flash Devices
v1.1
8 - 15
The procedure is as follows:
1. Select the bank to which you want VCCI to be assigned from the Choose Bank list.
2. Select the I/O standards for that bank. If you select any standard, the tool will automatically
show all compatible standards that have a common VCCI voltage requirement.
3. Click Apply.
find out how many I/O banks are needed for VCCI bank assignment.
Manually Assigning VREF Pins
Voltage-referenced inputs require an input reference voltage (VREF). The user must assign VREF pins
before running Layout. Before assigning a VREF pin, the user must set a VREF technology for the
bank to which the pin belongs.
VREF Rules for the Implementation of Voltage-Referenced I/O
Standards
The VREF rules are as follows:
1. Any I/O (except JTAG I/Os) can be used as a VREF pin.
2. One VREF pin can support up to 15 I/Os. It is recommended, but not required, that eight of
them be on one side and seven on the other side (in other words, all 15 can still be on one
side of VREF).
3. SSTL3 (I) and (II): Up to 40 I/Os per north or south bank in any position
4. LVPECL / GTL+ 3.3 V / GTL 3.3 V: Up to 48 I/Os per north or south bank in any position
5. SSTL2 (I) and (II) / GTL+ 2.5 V / GTL 2.5 V: Up to 72 I/Os per north or south bank in any
position.
6. VREF minibanks partition rule: Each I/O bank is physically partitioned into VREF minibanks.
The VREF pins within a VREF minibank are interconnected internally, and consequently, only
one VREF voltage can be used within each VREF minibank. If a bank does not require a VREF
signal, the VREF pins of that bank are available as user I/Os.
7. The first VREF minibank includes all I/Os starting from one end of the bank to the first power
triple and eight more I/Os after the power triple. Therefore, the first VREF minibank may
contain (0 + 8), (2 + 8), (4 + 8), (6 + 8), or (8 + 8) I/Os.
The second VREF minibank is adjacent to the first VREF minibank and contains eight I/Os, a
power triple, and eight more I/Os after the triple. An analogous rule applies to all other VREF
minibanks but the last.
The last VREF minibank is adjacent to the previous one but contains eight I/Os, a power
triple, and all I/Os left at the end of the bank. This bank may also contain (8 + 0), (8 + 2),
(8 + 4), (8 + 6), or (8 + 8) available I/Os.
Example:
4 I/Os
→ Triple → 8 I/Os, 8 I/Os → Triple → 8 I/Os, 8 I/Os → Triple → 2 I/Os
i.e., minibank A = (4 + 8) I/Os, minibank B = (8 + 8) I/Os, minibank C = (8 + 2) I/Os
Assigning the VREF Voltage to a Bank
When importing the PDC file, the VREF voltage can be assigned to the I/O bank. The PDC command
is as follows:
set_iobank –vref [value]
Another method for assigning VREF is by using MVN > Edit > I/O Bank Settings (Figure 8-14 on