TB9100 Reciter Service Manual
Network Circuitry
63
© Tait Electronics Limited January 2006
Address
Multiplexing and
Command Codes
Like other DRAM types, SDRAMs use multiplexed address inputs (A0 -
A11) to reduce the number of package pins. Initially the row addresses
(usually the higher order addresses) are latched from the address inputs, then
the column addresses (lower order addresses) are latched. The row addresses
are latched into the SDRAM by the row address strobe, RAS, while the
column address are latched by the column address strobe, CAS.
The multiplexing of the address lines is performed within the MPC under
the control of UPMA (see
“User-Programmable Machines” on page 51
).
The UPM also generates the row address strobe and column address strobe
at the appropriate times.
Unlike other DRAM types, SDRAMs also use the multiplexed address
lines, in conjunction with the control lines, to enter command codes
(
Table 5.11
) and SDRAM mode settings.
V = valid address, L= low, H = high, X = don’t care
SDRAM
Initialisation
After power up, the SDRAM chips must be initialized and set to their
correct operating mode before being used. Prior to setting the operating
mode, the internal nodes in the SDRAM must be stabilized to their normal
working voltages. After a time delay of 200us from power up, a precharge all
banks command is executed to set up the internal nodes for subsequent
memory cycles. Then, at least 8 refresh cycles (see
“SDRAM Refresh
Cycles” on page 64
) must be executed. Finally, the mode register set
command is issued to set the following parameters:
Table 5.11
SDRAM Command Codes
Code
Function
Control and Address Inputs
A0-
A11
A10
CS
RAS
CAS
WE
ACT
Bank activate
V
V
L
L
H
H
BST
Burst stop
X
X
L
H
H
L
DESL
Device deselect
X
X
H
X
X
X
MRS
Mode register set
V
V
L
L
L
L
NOP
No operation
X
X
L
H
H
H
PALL
Precharge all banks
X
H
L
L
H
L
PRE
Precharge selected bank
V
L
L
L
H
L
READ
Read access to one bank
V
L
L
H
L
H
READA
Read access with auto-precharge
V
H
L
H
L
H
REF
Auto-refresh
X
X
L
L
L
H
WRITE
Write access to one bank
V
L
L
H
L
L
WRITEA
Write access with auto-precharge
V
H
L
H
L
L
Summary of Contents for TB9100
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