Altera OCT - Manual (Page 3)

Features
The following figure shows the top-level diagram of the Altera OCT megafunction.
Figure 1: Altera OCT Megafunction Top-Level Diagram
OCT Block OCT Logic rzqin
Altera OCT
The Altera OCT megafunction provides the following features:
• RZQ pin—Dual-purpose pin. When used with OCT, the pin connects to an external reference resistor
to calculate the calibration codes to implement the required impedance.
• OCT block—Generates and sends calibration code words to the I/O buffer blocks.
• OCT logic—Receives the calibration code words serially from the OCT block and sends the calibration
code words in parallel to the buffers.
RZQ Pin
Each OCT block has one RZQ pin. RZQ pins are dual-purpose, which means that if the pins are not connected
to the OCT block, you can use the pins as regular I/O pins. Calibrated pins must have the same VCCIO as
the OCT block and the RZQ pin. Calibrated pins connected to the same OCT block must have the same
series and parallel termination values. You can apply location constraints on the RZQ pins to determine the
placement of the OCT block because the RZQ pin can only be connected to its corresponding OCT block.
OCT Block
The OCT block is a component that generates calibration codes to terminate the I/Os. When calibrating,
the OCT matches the impedance seen on the external resistor through the rzqin port. Then, the OCT
block generates two 16-bit calibration code words; one word calibrates the series termination while the other
calibrates the parallel termination. A dedicated bus serially sends the words to the OCT logic.
OCT Logic
The following figure shows the internals of an OCT logic.
Altera Corporation Altera OCT Megafunction User Guide
Feedback
3 Features
ug-altera_oct
2013.11.29