NEC uPD98502 - page 211

CHAPTER 3 SYSTEM CONTROLLER
Preliminary User’s Manual S15543EJ1V0UM 211
3.4.9 SDPTR (SDRAM Precharge Timing Register)
The SDRAM precharge timing register “SDPTR” is a read-write and 32-bit word-aligned register. SDPTR is used to
set the precharge timing for the SDRAM controller. SDPTR is initialized to 142H at reset and contains the following
fields:
Bits Field R/W Default Description
31:9 Reserved R/W 0 Hardwired to 0.
Input data -> precharge command timing (tDPL):8DPL R/W1
0 = 1 clock
1 = 2 clocks (default)
66 MHz: 15.2 ns
66 MHz: 30.3 ns
100 MHz: 10 ns
100 MHz: 20 ns
7 Reserved R/W 0 Hardwired to 0.
6:4 APT R/W 100 Active comm and -> precharge command timing (tRAS):
000 = 4 clocks
001 = 5 clocks
010 = 6 clocks
011 = 7 clocks
100 = 8 clocks (default)
101 = reserved
110 = reserved
111 = reserved
66 MHz: 60.6 ns
66 MHz: 75.7 ns
66 MHz: 90.9 ns
66 MHz: 106.0 ns
66 MHz: 121.2 ns
100 MHz: 40 ns
100 MHz: 50 ns
100 MHz: 60 ns
100 MHz: 70 ns
100 MHz: 80 ns
3:2 Reserved R/W 0 Hardwired to 0.
Precharge command -> active command timing (tRP):1:0 PAT R/W 10
00 = 2 clocks
01 = 3 clocks
10 = 4 clocks (default)
11 = reserved
66 MHz: 30.3 ns
66 MHz: 45.5 ns
66 MHz: 60.6 ns
100 MHz: 20 ns
100 MHz: 30 ns
100 MHz: 40 ns
Remark Don’t set the reserved value to each field in this register.
3.4.10 SDRMR (SDRAM Refresh Mode Register)
The SDRAM refresh mode register “SDRMR” is a read-write and 32-bit word-aligned register. SDRMR is used to
initialize the SDRAM refresh controller. SDRMR is initialized to 200H at reset and contains the following fields:
Bits Field R/W Default Description
31:16 Reserved R/W 0 Hardwired to 0.
15:0 RCSET R/W 0200H Reload value for SDRAM refresh timer counter.
This value, in system clock ticks, is automatically reloaded into the refresh
timer counter after the counter reached zero. The refresh timer counter
counts down from this value. Thus, time of the count cycle corresponds to 1
plus this filed value. The default value (200H = 512) is the refresh rate for an
SDRAM chip that requires 4096 refresh cycles every 32 ms (ex. one refresh
every 7.8125
µ
s) for system clock running at 66 MHz. This is very
conservative but it allows for successful boot, after which the reload value
can be increased. RCSET [7:0] is hardwired to 0, thus the timer value less
than 100H cannot be set this field. If such value is set into this field, the
default value “200H” is automatically loaded.