2.3.3 I/O Banks and Compatibility
Since each I/O bank has its own user-assigned input reference voltage (VREF) and an input/output supply voltage (VCCI), only I/Os with compatible standards can be assigned to the same bank.
The following table shows the compatible I/O standards for a common VREF (for voltage-referenced standards).
| VREF | Compatible Standards |
|---|---|
| 1.5V | SSTL 3 (Class I and II) |
| 1.25V | SSTL 2 (Class I and II) |
| 1.0V | GTL+ (2.5V and 3.3V Outputs) |
| 0.75V | HSTL (Class I) |
The following table shows compatible standards for a common VCCI.
| VCCI1 | Compatible Standards | VREF |
|---|---|---|
| 3.3V | LVTTL, PCI, PCI-X, LVPECL, GTL+ 3.3V | 1.0 |
| 3.3V | SSTL 3 (Class I and II), LVTTL, PCI, LVPECL | 1.5 |
| 2.5V | LVCMOS 2.5V, GTL+ 2.5V, LVDS2 | 1.0 |
| 2.5V | LVCMOS 2.5V, SSTL 2 (Classes I and II), LVDS2 | 1.25 |
| 1.8V | LVCMOS 1.8V | N/A |
| 1.5V | LVCMOS 1.5V, HSTL Class I | 0.75 |
- VCCI is used for both inputs and outputs
- VCCI tolerance is ±5%
The following table summarizes the different combinations of voltages and I/O standards that can be used together in the same I/O bank.
| I/O Standard | LVTTL 3.3V | LVCMOS 2.5V | LVCMOS 1.8V | LVCMOS 1.5V (JESD8-11) | 3.3V PCI/PCI-X | GTL+ (3.3V) | GTL+ (2.5V) | HSTL Class I (1. 5V) | SSTL2 Class I & II (2.5V) | SSTL3 Class I & II (3.3V) | LVDS (2.5V) | LVPECL (3.3V) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| LVTTL 3.3V (VREF=1.0V) | ✓ | — | — | — | ✓ | ✓ | — | — | — | — | — | ✓ |
| LVTTL 3.3V (VREF=1.5V) | ✓ | — | — | — | ✓ | — | — | — | — | ✓ | — | ✓ |
| LVCMOS 2.5V (VREF=1.0V) | — | ✓ | — | — | — | — | ✓ | — | — | — | ✓ | — |
| LVCMOS 2.5V (VREF=1.25V) | — | ✓ | — | — | — | — | — | — | ✓ | — | ✓ | — |
| LVCMOS 1.8V | — | — | ✓ | — | — | — | — | — | — | — | — | — |
| LVCMOS 1.5V (VREF = 1.75V) (JESD8-11) | — | — | — | ✓ | — | — | — | ✓ | — | — | — | — |
| 3.3V PCI/PCI-X (VREF = 1.0V) | ✓ | — | — | — | ✓ | ✓ | — | — | — | — | — | ✓ |
| 3.3V PCI/PCI-X (VREF = 1.5V) | ✓ | — | — | — | ✓ | — | — | — | — | ✓ | — | ✓ |
| GTL+ (3.3V) | ✓ | — | — | — | ✓ | ✓ | — | — | — | — | — | ✓ |
| GTL+ (2.5V) | — | ✓ | — | — | — | — | ✓ | — | — | — | — | — |
| HSTL Class I | — | — | — | ✓ | — | — | — | ✓ | — | — | — | — |
| SSTL2 Class I & II | — | ✓ | — | — | — | — | — | — | ✓ | — | ✓ | — |
| SSTL3 Class I & II | ✓ | — | — | — | ✓ | — | — | — | — | ✓ | — | ✓ |
| LVDS (VREF = 1.0V) | — | ✓ | — | — | — | — | ✓ | — | — | — | ✓ | — |
| LVDS (VREF = 1.25V) | — | ✓ | — | — | — | — | — | — | ✓ | — | ✓ | — |
| LVPECL (VREF = 1.0V) | ✓ | — | — | — | ✓ | ✓ | — | — | — | — | — | ✓ |
| LVPECL (VREF = 1.5V) | ✓ | — | — | — | ✓ | — | — | — | — | ✓ | — | ✓ |
The GTL+ 2.5V is not supported across the full military temperature range.
A tick symbol indicates whether standards can be used within a bank at the same time Examples:
- LVTTL can be used with 3.3V PCI and GTL+ (3.3V), when VREF = 1.0V (GTL+ requirement).
- LVTTL can be used with 3.3V PCI and SSTL3 Class I and II, when VREF = 1.5V (SSTL3 requirement).
The two I/O standards are compatible if:
- Their VCCI values are identical
- Their VREF standards are identical (if applicable)
For example, if LVTTL 3.3V (VREF= 1.0V) is used, then the other available (that is compatible) I/O standards in the same bank are LVTTL 3.3V PCI/PCI-X, GTL+, and LVPECL.
Also, when multiple I/O standards are used within a bank, the voltage tolerance will be limited to the minimum tolerance of all I/O standards used in the bank.