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Intel
IXP1250 Network Processor
138
Datasheet
4.3.9.3
SDRAM Signal Protocol
This section describes the SDRAM timing parameters referenced in the SDRAM timing diagrams
that follow. This nomenclature is consistent with most JEDEC standard SDRAM devices.
tRP
tRP is the minimum number of cycles after a precharge cycle that a bank may be opened (or
"RASd"). The
IXP1200 Network Processor Family Micrcode Programmer
’
s Reference Manual
refers to this as the tRP Precharge Time. Also referred to as
“
PRECHARGE command period
”
in
SDRAM datasheets.
tRASmin
tRASmin is the minimum number of cycles that a bank must be open before it can be closed using
a precharge command. The maximum time that a bank may be open, tRASmax, is not checked,
because the IXP1250 SDRAM Controller methodology is to close all banks after the usage is
complete. The
IXP1200 Network Processor Family Micrcode Programmer
’
s Reference Manual
refers to this as the tRASmin Active Command Period. Also referred to as
“
ACTIVE to
PRECHARGE command period
”
in SDRAM datasheets.
tRCD
tRCD is the number of cycles between the bank opening (or "RAS") and any read or write
command (or "CAS"). The
IXP1200 Network Processor Family Micrcode Programmer
’
s
Reference Manual
refers to this as the tRCD RAS to CAS Delay. Also referred to as
“
ACTIVE to
READ or WRITE delay
”
in SDRAM datasheets.
tRRD
tRRD is the number of cycles between successive bank openings, or RAS cycles. The
IXP1200
Network Processor Family Micrcode Programmer
’
s Reference Manual
refers to this as the tRRD
Bank to Bank Delay Time. Also referred to as
“
ACTIVE bank A to ACTIVE bank B command
”
in
SDRAM datasheets.
tRC
tRC is the SDRAM bank cycle time, indicating that the minimum time that a command may be
active. For most cases, this is the sum of tRP and tRASmin, although there are some SDRAM data
sheets where the absolute time for tRC (in ns) is not equal to the sum (in ns) of tRP and tRASmin.
In these cases, typically when rounding up to an even number of clock cycles, they are equivalent.
Since the SDRAM Controller CSRs are programmed with a number of clock cycles, these
Table 52. Signal Delay Deratings for T
val
and T
ctl
Signal
Maximum Derating (ns/pF)
(IX Bus Speed)
Minimum Derating (ns/pF)
(IX Bus Speed)
83 MHz
100 MHz
116 MHz
83 MHz
100 MHz
116 MHz
SDCLK
0.053
—
—
0.025
—
—
DQM
0.065
0.06
0.031
0.03
0.025
0.015
WE_L
0.065
0.06
0.031
0.03
0.025
0.015
RAS_L
0.065
0.06
0.031
0.03
0.025
0.015
CAS_L
0.065
0.06
0.031
0.03
0.025
0.015
MADR[14:0]
0.065
0.06
0.031
0.03
0.025
0.015
MDATA[63:0]
0.095
0.09
0.035
0.03
0.025
0.015
MDATA_ECC[7:0]
0.095
0.09
0.035
0.03
0.025
0.015