Uncalibrated Source Termination in HP I/O Banks - Uncalibrated Source Termination in HP I/O Banks - UG861

HP I/O banks have an optional uncalibrated source termination feature for SSTL, HSTL, POD, and HSUL standards that is similar to DCI. This feature provides an option of a 40 Ω, 48 Ω, or 60 Ω driver for the supported standards to match the characteristic impedance of the driven line.

An important difference between this uncalibrated option and DCI is that instead of calibrating to an external reference resistor on the VRP pin when using DCI, the uncalibrated source termination feature invokes internal resistors determined by the OUTPUT_IMPEDANCE attribute where no calibration routine is available to compensate for temperature, process, or voltage variations.

The allowed values for OUTPUT_IMPEDANCE are RDRV_40_40, RDRV_48_48, or RDRV_60_60.

The main difference in how DCI or uncalibrated termination is invoked in a design is determined when choosing to use either a DCI I/O standard or an uncalibrated one. In both DCI and uncalibrated I/O standards, source termination value is determined by the attribute OUTPUT_IMPEDANCE.

The following table shows a list of I/O standards that support uncalibrated source termination in HP I/O banks.