24LCS21A
1K 2.5V Dual Mode I
2
C
™
Serial EEPROM
FEATURES
• Single supply with operation down to 2.5V
• Completely implements DDC1
™
/DDC2
™
interface for monitor identification, including
recovery to DDC1
• Low power CMOS technology
- 1 mA typical active current
- 10
µ
A standby current typical at 5.5V
• 2-wire serial interface bus, I
2
C
™
compatible
• 100 kHz (2.5V) and 400 kHz (5V) compatibility
• Self-timed write cycle (including auto-erase)
• Hardware write-protect pin
• Page-write buffer for up to eight bytes
• 10,000,000 erase/write cycles guaranteed
• Data retention > 200 years
• ESD Protection > 4000V
• 8-pin PDIP and SOIC package
• Available for extended temperature ranges
- Commercial (C):
0
°
C to +70
°
C
- Industrial (I):
-40
°
C to +70
°
C
PACKAGE TYPES
PDIP
NC
NC
WP
V
SS
1
24LCS21A
2
3
4
8
7
6
5
V
CC
VCLK
SCL
SDA
SOIC
NC
NC
WP
V
SS
1
24LCS21A
2
3
4
8
7
6
5
V
CC
VCLK
SCL
SDA
DESCRIPTION
The Microchip Technology Inc. 24LCS21A is a 128 x 8-
bit dual-mode Electrically Erasable PROM. This device
is designed for use in applications requiring storage
and serial transmission of configuration and control
information. Two modes of operation have been imple-
mented: Transmit-Only Mode and Bi-directional Mode.
Upon power-up, the device will be in the Transmit-Only
Mode, sending a serial bit stream of the memory array
from 00h to 7Fh, clocked by the VCLK pin. A valid high
to low transition on the SCL pin will cause the device to
enter the transition mode, and look for a valid control
byte on the I
2
C bus. If it detects a valid control byte from
the master, it will switch into Bi-directional Mode, with
byte selectable read/write capability of the memory
array using SCL. If no control byte is received, the
device will revert to the Transmit-Only Mode after it
receives 128 consecutive VCLK pulses while the SCL
pin is idle. The 24LCS21A also enables the user to
write-protect the entire memory array using its write-
protect pin. The 24LCS21A is available in a standard
8-pin PDIP and SOIC package in both commercial and
industrial temperature ranges.
BLOCK DIAGRAM
WP
HV GENERATOR
I/O
CONTROL
LOGIC
MEMORY
CONTROL
LOGIC
XDEC
EEPROM
ARRAY
PAGE LATCHES
SDA
SCL
YDEC
VCLK
V
CC
V
SS
SENSE AMP
R/W CONTROL
DDC is a trademark of the Video Electronics Standards Association.
I
2
C is a trademark of Philips Corporation.
©
1996 Microchip Technology Inc.
Preliminary
This document was created with FrameMaker 4 0 4
DS21161C-page 1
24LCS21A
1.0
1.1
ELECTRICAL
CHARACTERISTICS
Maximum Ratings*
TABLE 1-1:
Name
WP
V
SS
SDA
SCL
VCLK
V
CC
NC
PIN FUNCTION TABLE
Function
Write Protect (active low)
Ground
Serial Address/Data I/O
Serial Clock (Bi-directional Mode)
Serial Clock (Transmit-Only Mode)
+2.5V to 5.5V Power Supply
No Connection
V
CC
........................................................................7.0V
All inputs and outputs w.r.t. V
SS
.... -0.6V to V
CC
+1.0V
Storage temperature ..........................-65
°
C to +150
°
C
Ambient temp. with power applied .....-65
°
C to +125
°
C
Soldering temperature of leads (10 seconds) .. +300
°
C
ESD protection on all pins
..................................... ≥
4 kV
*Notice:
Stresses above those listed under “Maximum ratings”
may cause permanent damage to the device. This is a stress rat-
ing only and functional operation of the device at those or any
other conditions above those indicated in the operational listings
of this specification is not implied. Exposure to maximum rating
conditions for extended periods may affect device reliability.
TABLE 1-2:
DC CHARACTERISTICS
V
CC
= +2.5V to 5.5V
Commercial (C): Tamb = 0
°
C to +70
°
C
Industrial (I):
Tamb =-40
°
C to +85
°
C
Parameter
SCL and SDA pins:
High level input voltage
Low level input voltage
Input levels on VCLK pin:
High level input voltage
Low level input voltage
Hysteresis of Schmitt trigger inputs
Low level output voltage
Low level output voltage
Input leakage current
Output leakage current
Pin capacitance (all inputs/outputs)
Operating current
Standby current
Note:
Symbol
V
IH
V
IL
V
IH
V
IL
V
HYS
V
OL1
V
OL2
I
LI
I
LO
Cin, Cout
I
CC
Write
I
CC
Read
I
CCS
Min
0.7 V
CC
—
2.0
—
.05 V
CC
—
—
-10
-10
—
—
—
—
—
Max
—
0.3 V
CC
—
0.2 V
CC
—
0.4
0.6
10
10
10
3
1
30
100
Units
V
V
V
V
V
V
V
µ
A
µ
A
pF
mA
mA
µ
A
µ
A
V
CC
≥
2.7V (Note)
V
CC
< 2.7V (Note)
(Note)
I
OL
= 3 mA, V
CC
= 2.5V (Note)
I
OL
= 6 mA, V
CC
= 2.5V
V
IN
= 0.1V to V
CC
V
OUT
= 0.1V to V
CC
V
CC
= 5.0V (Note)
Tamb = 25
°
C, F
CLK
= 1 MHz
V
CC
= 5.5V
V
CC
= 5.5V, SCL = 400 kHz
V
CC
= 3.0V, SDA = SCL = V
CC
V
CC
= 5.5V, SDA = SCL = V
CC
Conditions
This parameter is periodically sampled and not 100% tested.
DS21161C-page 2
Preliminary
©
1996 Microchip Technology Inc.
24LCS21A
TABLE 1-3:
AC CHARACTERISTICS
Vcc= 2.5-4.5V
Standard Mode
Min
Clock frequency
Clock high time
Clock low time
SDA and SCL rise time
SDA and SCL fall time
F
CLK
T
HIGH
T
LOW
T
R
T
F
—
4000
4700
—
—
4000
4700
0
250
4000
—
4700
Max
100
—
—
1000
300
—
—
—
—
—
3500
—
Vcc= 4.5 - 5.5V
Fast Mode
Min
—
600
1300
—
—
600
600
0
100
600
—
1300
Max
400
—
—
300
300
—
—
—
—
—
900
—
kHz
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
Parameter
Symbol
Units
Remarks
(Note 1)
(Note 1)
After this period the first clock
pulse is generated
Only relevant for repeated
START condition
(Note 2)
START condition hold time T
HD
:
STA
START condition setup
time
Data input hold time
T
SU
:
STA
T
HD
:
DAT
Data input setup time
T
SU
:
DAT
STOP condition setup time T
SU
:
STO
Output valid from clock
T
AA
Bus free time
T
BUF
(Note 2)
Time the bus must be free
before a new transmission
can start
(Note 1), C
B
≤
100 pF
(Note 3)
Byte or Page mode
Output fall time from V
IH
T
OF
minimum to V
IL
maximum
Input filter spike suppres-
T
SP
sion (SDA and SCL pins)
Write cycle time
T
WR
Transmit-Only Mode Parameters
Output valid from VCLK
T
VAA
VCLK high time
T
VHIGH
VCLK low time
T
VLOW
VCLK setup time
T
VHST
VCLK hold time
T
SPVL
Mode transition time
T
VHZ
Transmit-Only power up
T
VPU
time
Input filter spike suppres-
T
SPV
sion (VCLK pin)
Endurance
—
—
—
—
—
4000
4700
0
4000
—
0
—
10M
250
50
10
2000
—
—
—
—
1000
—
100
—
20 +
0.1 C
B
—
—
—
600
1300
0
600
—
0
—
10M
250
50
10
1000
—
—
—
—
500
—
100
—
ns
ns
ms
ns
ns
ns
ns
ns
ns
ns
ns
cycles
25°C, Vcc = 5.0V, Block Mode
(Note 4)
Note 1: Not 100% tested. C
B
= Total capacitance of one bus line in pF.
2: As a transmitter, the device must provide an internal minimum delay time to bridge the undefined region (min-
imum 300 ns) of the falling edge of SCL to avoid unintended generation of START or STOP conditions.
3: The combined T
SP
and V
HYS
specifications are due to Schmitt trigger inputs which provide noise and spike
suppression. This eliminates the need for a T
I
specification for standard operation.
4: This parameter is not tested but guaranteed by characterization. For endurance estimates in a specific appli-
cation, please consult the Total Endurance Model which can be obtained on our BBS or website.
©
1996 Microchip Technology Inc.
Preliminary
DS21161C-page 3
24LCS21A
2.0
FUNCTIONAL DESCRIPTION
The 24LCS21A is designed to comply to the DDC Stan-
dard proposed by VESA (Figure 3-3) with the exception
that it is not Access.bus capable. It operates in two
modes, the Transmit-Only Mode and the Bi-directional
Mode. There is a separate 2-wire protocol to support
each mode, each having a separate clock input but
sharing a common data line (SDA). The device enters
the Transmit-Only Mode upon power-up. In this mode,
the device transmits data bits on the SDA pin in
response to a clock signal on the VCLK pin. The device
will remain in this mode until a valid high to low transi-
tion is placed on the SCL input. When a valid transition
on SCL is recognized, the device will switch into the Bi-
directional Mode and look for its control byte to be sent
by the master. If it detects its control byte, it will stay in
the Bi-directional Mode. Otherwise, it will revert to the
Transmit-Only Mode after it sees 128 VCLK pulses.
mit-Only Mode (Section 2.2). In this mode, data is
transmitted on the SDA pin in 8-bit bytes, with each byte
followed by a ninth, null bit (Figure 2-1). The clock
source for the Transmit-Only Mode is provided on the
VCLK pin, and a data bit is output on the rising edge on
this pin. The eight bits in each byte are transmitted most
significant bit first. Each byte within the memory array
will be output in sequence. After address 7Fh in the
memory array is transmitted, the internal address point-
ers will wrap around to the first memory location (00h)
and continue. The Bi-directional Mode Clock (SCL) pin
must be held high for the device to remain in the
Transmit-Only Mode.
2.2
Initialization Procedure
2.1
Transmit-Only Mode
The device will power up in the Transmit-Only Mode at
address 00H. This mode supports a unidirectional
2-wire protocol for continuous transmission of the
contents of the memory array. This device requires that
it be initialized prior to valid data being sent in the Trans-
After V
CC
has stabilized, the device will be in the
Transmit-Only Mode. Nine clock cycles on the VCLK pin
must be given to the device for it to perform internal
sychronization. During this period, the SDA pin will be
in a high impedance state. On the rising edge of the
tenth clock cycle, the device will output the first valid
data bit which will be the most significant bit in address
00h. (Figure 2-2).
FIGURE 2-1:
TRANSMIT-ONLY MODE
SCL
Tvaa
SDA
Bit 1 (LSB)
Tvaa
Null Bit
Bit 1 (MSB)
Bit 7
VCLK
Tvhigh Tvlow
FIGURE 2-2:
DEVICE INITIALIZATION
Vcc
SCL
High Impedance for 9 clock cycles
Tvpu
VCLK
1
2
8
9
10
11
Tvaa
Tvaa
Bit 8
Bit 7
SDA
DS21161C-page 4
Preliminary
©
1996 Microchip Technology Inc.
24LCS21A
3.0
BI-DIRECTIONAL MODE
Before the 24LCS21A can be switched into the Bi-
directional Mode (Figure 3-1), it must enter the transi-
tion mode, which is done by applying a valid high to low
transition on the Bi-directional Mode Clock (SCL). As
soon it enters the transition mode, it looks for a control
byte 1010 000X on the I
2
C™ bus, and starts to count
pulses on VCLK. Any high to low transition on the SCL
line will reset the count. If it sees a pulse count of 128
on VCLK while the SCL line is idle, it will revert back to
the Transmit-Only Mode, and transmit its contents start-
ing with the most significant bit in address 00h. How-
ever, if it detects the control byte on the I
2
C™ bus,
(Figure 3-2) it will switch to the in the Bi-directional
Mode. Once the device has made the transition to the
Bi-directional mode, the only way to switch the device
back to the Transmit-Only Mode is to remove power
from the device. The mode transition process is shown
in detail in Figure 3-3.
Once the device has switched into the Bi-directional
Mode, the VCLK input is disregarded, with the excep-
tion that a logic high level is required to enable write
capability. This mode supports a two-wire Bi-directional
data transmission protocol (I
2
C™). In this protocol, a
device that sends data on the bus is defined to be the
transmitter, and a device that receives data from the
bus is defined to be the receiver. The bus must be con-
trolled by a master device that generates the Bi-direc-
tional Mode Clock (SCL), controls access to the bus
and generates the START and STOP conditions, while
the 24LCS21A acts as the slave. Both master and
slave can operate as transmitter or receiver, but the
master device determines which mode is activated. In
the Bi-directional mode, the 24LCS21A only responds
to commands for device 1010 000X.
FIGURE 3-1:
MODE
SCL
MODE TRANSITION WITH RECOVERY TO TRANSMIT-ONLY MODE
Transmit
Only
Bi-directional
TVHZ
Recovery to Transmit-Only Mode
(MSB of data in 00h)
SDA
VCLK count =
VCLK
1
2
3
4
127 128
Bit8
FIGURE 3-2:
SUCCESSFUL MODE TRANSITION TO BI-DIRECTIONAL MODE
Transition Mode with possibility to return to Transmit-Only Mode
Bi-directional
permanently
Transmit
Only Mode
MODE
SCL
SDA
VCLK count =
VCLK
1
2
S
n
0
1
0
1
0
0
0
0
0
ACK
n < 128
©
1996 Microchip Technology Inc.
Preliminary
DS21161C-page 5
