DS1222
BankSwitch Chip
www.dalsemi.com
FEATURES
Provides bank switching for 16 banks of
memory
Bank switching is software-controlled by a
pattern recognition sequence on four address
inputs
Automatically sets all 16 banks off on
power-up
Bank switching logic allows only one bank on
at a time
Custom recognition patterns are available to
prevent unauthorized access
Full
±10%
operating range
Low-power CMOS circuitry
Can be used to expand the address range of
microprocessors and decoders
Optional 16-pin SOIC surface mount package
PIN ASSIGNMENT
CEI
PFI
AW
AX
AY
AZ
GND
1
2
3
4
5
6
7
14
13
12
11
10
9
8
V
CC
CEO
BS1
BS2
BS3
BS4
NC
CEI
NC
PFI
AW
AX
AY
AZ
GND
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
V
CC
CEO
NC
BS1
BS2
BS3
NC
BS4
DS1222 14-Pin DIP
(300-mil)
See Mech. Drawings
Section
DS1222S 16-Pin SOIC
(300-mil)
See Mech. Drawings
Section
PIN DESCRIPTION
A
W
-A
Z
CEI
CEO
NC
BS1,BS2,
BS3,BS4
PFI
V
CC
GND
- Address Inputs
- Chip Enable Input
- Chip Enable Output
- No Connection
- Bank Select Outputs
- Bank Select Outputs
- Power Fail Input
- +5 Volts
- Ground
DESCRIPTION
The DS1222 BankSwitch Chip is a CMOS circuit designed to select one of 16 memory banks under
software control. Memory bank switching allows for an increase in memory capacity without additional
address lines. Continuous blocks of memory are enabled by selecting proper memory bank through a
pattern recognition sequence on four address inputs. Custom patterns from Dallas Semiconductor can
provide security through uniqueness and prevent unauthorized access. By combining the DS1222 with
the DS1212 Nonvolatile Controller x16 Chip, up to 16 banks of static RAMs can be selected.
1 of 4
111899
DS1222
OPERATION - BANK SWITCHING
Initially, on power-up all four bank select outputs are low and the chip enable output (
CEO
) is held high.
(Note: the power fail input [
PFI
] must be low prior to power-up to assure proper initialization.) Bank
switching is achieved by matching a predefined pattern stored within the DS1222 with a 16-bit sequence
received on four address inputs. Prior to entering the 16-bit pattern, which sets the bank switch, a read
cycle of 1111 on address inputs AW through AZ should be executed to guarantee that pattern entry starts
with bit 0. Each set of address inputs is clocked into the DS1222 when
CEI
is driven low. All 16 inputs
must be consecutive read cycles. The first eleven cycles must match the exact bit pattern as shown in
Table 1. The last five cycles must match the exact bit pattern as shown for addresses AX, AY, and AZ.
However, address line AW defines the bank number to be enabled as per Table 2.
Switching to a selected bank of memory occurs on the rising edge of
CEI
when the last set of bits is input
and a match has been established. After bank selection
CEO
always follows
CEI
with a maximum
propagation delay of 15 ns. The bank selected is determined by the levels set on Bank Select 1 through
Bank Select 4 as per Table 2. These levels are held constant for all memory cycles until a new memory
bank is selected.
ADDRESS BIT SEQUENCE
Table 1
BIT SEQUENCE
ADDRESS
INPUTS
A
W
A
X
A
Y
A
Z
0
1
0
1
0
1
0
1
0
1
2
1
0
1
0
3
0
1
0
1
4
0
1
0
1
5
0
1
0
1
6
1
0
1
0
7
1
0
1
0
8
0
1
0
1
9
1
0
1
0
10
0
1
0
1
11
x
0
1
0
12
x
0
1
0
13
x
0
1
0
14
x
1
0
15
x
1
0
1
1
X See Table 2
BANK SELECT CONTROL
Table 2
Bank
Selected
*Banks Off
Bank 0
Bank 1
Bank 2
Bank 3
Bank 4
Bank 5
Bank 6
Bank 7
Bank 8
Bank 9
Bank 10
Bank 11
Bank 12
Bank 13
Bank 14
Bank 15
A
W
Bit Sequence
11
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
12
X
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
13
X
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
14
X
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
15
X
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
BS1
Low
Low
High
Low
High
Low
High
Low
High
Low
High
Low
High
Low
High
Low
High
Outputs
BS2
Low
Low
Low
High
High
Low
Low
High
High
Low
Low
High
High
Low
Low
High
High
BS3
Low
Low
Low
Low
Low
High
High
High
High
Low
Low
Low
Low
Low
High
High
High
BS4
Low
Low
Low
Low
Low
Low
Low
Low
Low
High
High
High
High
High
High
High
High
*
CEO
=V
IH
independent of
CEI
2 of 4
DS1222
ABSOLUTE MAXIMUM RATINGS*
Voltage on any Pin Relative to Ground
Operating Temperature
Storage Temperature
∗
-0.3V to +7.0V
0°C to 70°C
-55°C to +125°C
This is a stress rating only and functional operation of the device at these or any other conditions
above those indicated in the operation sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods of time may affect reliability.
RECOMMENDED DC OPERATING CONDITIONS
PARAMETER
Power Supply Voltage
Logic 1
Logic 0
SYMBOL
V
CC
V
IH
V
IL
MIN
4.5
2.2
-0.3
TYP
5.0
MAX
5.5
V
CC
+0.3
+0.8
(0°C to 70°C)
UNITS
V
V
V
NOTES
1
1
1
DC ELECTRICAL CHARACTERISTICS
PARAMETER
Input Leakage Current
I/O Leakage Current
Output Current @ 2.4V
Output Current @ 0.4V
Operating Current
SYMBOL
I
IL
I
LO
I
OH
I
OL
I
CC
MIN
-1.0
-1.0
-1.0
(0°C to 70°C; V
CC
= 5V
±10%)
TYP
MAX
+1.0
+1.0
+4.0
15
UNITS
µA
µA
mA
mA
mA
NOTES
2
2
CAPACITANCE
PARAMETER
Input Capacitance
Input/Output Capacitance
SYMBOL
C
IN
C
I/O
MIN
TYP
5
5
MAX
10
10
(T
A
= 25°C)
UNITS
pF
pF
NOTES
AC ELECTRICAL CHARACTERISTICS
PARAMETER
Address Setup
Address Hold
Read Recovery
Propagation Delay
Power Fail Input to First
CEI
Chip Enable Low
SYMBOL
t
AS
t
AH
t
RR
t
PD
t
PF
t
CW
MIN
5
50
40
50
110
(0°C to 70°C; V
CC
= 5V
±10%)
TYP
MAX
UNITS
ns
ns
ns
ns
ns
ns
NOTES
15
2
NOTES:
1. All voltages are referenced to ground.
2. Measured with a load as shown in Figure 1.
3 of 4
DS1222
OUTPUT LOAD
Figure 1
TIMING DIAGRAM-ACCESS TO BANK SWITCH
4 of 4
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