Supported Use Cases
402
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
DDR2/mDDR Memory Controller
Configuring DDR PHY Control Register (DRPYC1R)
The DDR PHY control register (DRPYC1R) contains a read latency (RL) field that helps the DDR2/mDDR
memory controller determine when to sample read data. The RL field should be programmed to a value
equal to the CAS latency plus the round trip board delay minus 1. The minimum RL value is CAS latency
plus 1 and the maximum RL value is CAS latency plus 2 (again, the RL field would be programmed to
these values minus 1).
shows the resulting DRPYC1R configuration.
When calculating round trip board delay the signals of primary concern are the differential clock signals
(DDR_CLK and DDR_CLK) and data strobe signals (DDR_DQS). For these signals, calculate the round
trip board delay from the DDR memory controller to the memory and then choose the maximum delay to
determine the RL value. In this example, we will assume the round trip board delay is one DDR_CLK
cycle; therefore, RL can be calculated as:
RL = CAS l round trip board delay – 1 = 4 + 1 – 1 = 4
Table 14-20. DRPYC1R Configuration
Field
Value
Function Selection
EXT_STRBEN
1h
Programs to select external strobe gating
RL
4h
Read latency is equal to CAS latency plus round trip board delay for data minus 1
PWRDNEN
0
Programmed to power up the DDR2/mDDR memory controller receivers