
Brooktree
143
CONFIGURATION AND PLL REGISTER DEFINITIONS
Conguration and PLL Registers
L2166_A
Bt2166
Graphics/Video Controller
Memory Conguration
Register
name:
MEM_CFG
address:
GBASE | 00500014h, read/write
size:
32 bits
function:
The synchronous memory conguration register shown in Table 111
allows for optimum performance with different memories.
Table 111. Synchronous Memory Conguration Register (MEM_CFG)
(1 of 2)
Bit #
Name
Default
Value
Description
27:26
Reserved
0
Reserved, set to zero
25
tRAS_EXTEND
1
This bit extends the tRC and tRAS by one cycle for normal memory cycles
(non-refresh). This bit is independent of RFSH_CYCLE_CNT which is
used only for refresh cycles. Reset value: 1.
24
RESET_CFG
0
This bit causes the memory controller to perform another initialization
sequence similar to power on reset. When the memory controller deter-
mines that this bit has changed state (from 0 to a 1 or 1 to a 0), it will rein-
itialize the memory and rewrite the sync memory internal cong register
via the MRS command (see the documentation that accompanied the
specic memory device). The initialization sequence will be done at the
next refresh request. The memory refresh MUST be enabled in order to
use this function Reset value: 0.
23
Reserved
0
This bit is reserved for future use. Set to 0.
22
RAS_PRE_CNT
1
Congures the RAS precharge time (in cycles) used in the memory con-
troller. Reset value: 1.
1 = programs the memory controller for a RAS precharge of 3 cycles
0 = indicates a 2 cycle RAS precharge will be performed
21
RFSH_CYCLE_CNT
1
This bit controls the number of clocks that a refresh cycle will take to com-
plete a refresh operation (tRC). This affects only refresh cycles.
Reset value: 1.
1 = congures the memory controller for a refresh cycle count of 10 cycles
0 = congures the memory controller for a refresh cycle count of 9
20
RCD_CNT
1
This bit controls the number of cycles of the RAS to CAS delay.
Reset value: 1.
1 = congures the memory controller for a 3 cycle delay
0 = Not applicable in Bt2166 Rev A.
19
RBSTP_LATENCY
1
This bit controls the manner in which the BSTP (Burst Stop) command
operates with read operations to the memory. Reset value: 1.
1 = used for memory devices that tristate their output 3 clocks after receiv-
ing the BSTP command.
0 = used for memory devices that tristate their output 2 clocks after the
clock when a valid BSTP command is received.
18
WBSTP_LATENCY
0
This bit controls the manner in which the BSTP (Burst Stop) command
operates with write operations to the memory. Reset value: 0.
1 = used for memory devices that allow writing to the memory the same
cycle as the BSTP command and terminate the write burst the next
cycle.
0 = used for memory devices that prevent a write the same cycle as the
BSTP command.