
150
S71WS-Nx0 Based MCPs
S71WS-N_01_A4 September 15, 2005
A d v a n c e I n f o r m a t i o n
38 Mode Register Setting Operation
The device has several modes:
Asynchronous Page Read mode
Asynchronous Write mode
Synchronous Burst Read mode
Synchronous Burst Write mode
Standby mode and Partial Array Refresh (PAR) mode.
Partial Array Refresh (PAR) mode is defined through the Mode Register Set (MRS) option. The MRS
option also defines burst length, burst type, wait polarity and latency count at synchronous burst
read/write mode.
38.1
Mode Register Set (MRS)
The mode register stores the data for controlling the various operation modes of the pSRAM. It
programs Partial Array Refresh (PAR), burst length, burst type, latency count and various vendor
specific options to make pSRAM useful for a variety of different applications. The default values
of mode register are defined, therefore when the reserved address is input, the device runs at
default modes.
The mode register is written by driving CS#, ADV#, WE#, UB#, LB# and MRS# to V
IL
and driving
OE# to V
IH
during valid addressing. The mode register is divided into various fields depending on
the fields of functions. The PAR field uses A0–A4, Burst Length field uses A5–A7, Burst Type uses
A8, Latency Count uses A9–A11, Wait Polarity uses A13, Operation Mode uses A14–A15 and
Driver Strength uses A16–A17.
Refer to the Table below for detailed Mode Register Settings. A18–A22 addresses are “Don’t care”
in the Mode Register Setting.
Table 38.1 Mode Register Setting According to Field of Function
Note:
DS (Driver Strength), MS (Mode Select), WP (Wait Polarity), Latency (Latency Count), BT (Burst Type), BL (Burst
Length), PAR (Partial Array Refresh), PARA (Partial Array Refresh Array), PARS (Partial Array Refresh Size), RFU (Reserved
for Future Use).
Table 38.2 Mode Register Set
Address
Function
A17 – A16
DS
A15 – A14
MS
A13
WP
A12
RFU
A11 – A19
Latency
A8
BT
A7 – A5
BL
A4 – A3
PAR
A2
A1 – A0
PARS
PARA
Driver Strength
Mode Select
A17
0
0
1
A16
0
1
0
DS
A15
0
0
1
A14
0
1
0
MS
Full Drive (note 1)
1/2 Drive
1/4 Drive
Async. 4 Page Read / Async. Write (note 1)
Sync. Burst Read / Async. Write
Sync. Burst Read / Sync. Burst Write
WAIT# Polarity
RFU
Latency Count
A10
A9
Burst Type
Burst Length
A5
A13
WP
A12
RFU
Must
(note 1)
—
A11
Latency
A8
BT
A7
A6
BL
0
Low Enable (note 1)
0
0
0
0
3
0
Linear (note 1)
0
1
0
4 word
1
High Enable
1
0
0
0
0
1
1
1
0
1
4
5
6
1
Interleave
0
1
1
1
0
1
1
0
1
8 word
16 word (note 1)
Full (256 word)