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3–8 Chapter 3: Functional Description

ALTOCT Megafunction Ports

Dynamic Calibrated On-Chip Termination (ALTOCT) Megafunction February 2012 Altera Corporation

User Guide

In the simulation waveform shown in Figure 3–3, all of the calibration blocks have

their

calibration_request

signals asserted at a particular time. Initially, requests for

calibration are done simultaneously for calibration block[0] and

calibration_request[3]

. This can be observed in the behavior of the

calibration_request[3]

and

calibration_request[0]

signals. Both signals are

asserted and deasserted at the same time.

Observe the behavior of the

calibration_busy[3]

and

calibration_busy[0]

signals.

Notice that both are also asserted and deasserted at the same time. This is because

multiple OCT calibration blocks can be calibrated at the same time. When these

signals get deasserted, calibration is complete.

Next, observe the

cal_shift_busy[3]

and

cal_shift_busy[0]

signals. They are both

asserted at the same time as the

calibration_busy[3]

and

calibration_busy[0]

signals, and both signals get deasserted after a number of clock cycles. These signals

indicate the status of calibration and serial shifting of the termination codes.

Notice that the

cal_shift_busy[3]

and

cal_shift_busy[0]

signals get deasserted at

different time—

cal_shift_busy[0]

gets deasserted first and followed by

cal_shift_busy[3]

. This is because the shifting process is serial, and only one

calibration block can be active at a time. In the event of multiple calibration block

requests, the priority calibration block[x] is based on this order. x=0, 1, 2, 3, 4, 5, 6, 7, 8,

9, which means calibration block[0] shift codes first and then followed by the other

blocks in the order. Observe Figure 3–3, the

cal_shift_busy[0]

gets deasserted first

and then followed by

cal_shift_busy[3]

. This is because calibration block[0] has

higher priority than calibration block[3].

Finally, the calibrated codes must be converted from serial format to parallel format

before being used in the I/O buffers. This is done by asserting and deasserting the

s2pload[0]

and

s2pload[3]

signals for 1 clock cycle only after

cal_shift_busy[3]

and

cal_shift_busy[0]

signals have been deasserted. See Figure 3–3.

Similar calibration process as described on 3–7 applies to the remaining portion of the

waveform. However, it applies to calibration block[2] and calibration block[1].

ALTOCT Megafunction Ports

Table 3–2 and Table 3–3 lists the input and output ports for the ALTOCT

megafunction.

Input Ports

Table 3–2. ALTOCT Megafunction Input Ports

Port Name Required Description Comments

aclr

No Asynchronous clear If omitted, value is GND

calibration_request

Yes User request for calibration Input port

[OCT_BLOCK_NUMBER - 1..0]

wide

calibration_wait

Clock cycles to wait before

starting calibration after

calibration request

Input port

[OCT_BLOCK_NUMBER - 1..0]

wide. If omitted, value is GND

clock

Yes System clock –—

rdn

Yes

Pull-down reference

resistor

Input port

[OCT_BLOCK_NUMBER - 1..0]

wide

1 2 ... 10 11 12 13 14 15 16 17 18 19

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