Altera Dynamic Calibrated On-Chip Termination - Manual (Page 15)

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 No
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