Cirrus Logic AN225 - Manual

1
Copyright  Cirrus Logic, Inc. 2003
(All Rights Reserved)
www.cirrus.com
AN225
Application Note
USING THE CS5460A AUTO-BOOT MODE
1. Which EEPROMs Can Be Used?
Several industry-standard serial EEPROMs that
will successfully run auto-boot with the CS5460A
are listed below:
• Atmel
AT25010
AT25020
AT25040
• National Semiconductor
NM25C040M8
NM25020M8
• Xicor
X25040SI
These types of serial EEPROMs expect a specific
8-bit command word (00000011) in order to per-
form a memory download. The CS5460A has been
hardware programmed to transmit this 8-bit com-
mand word to the EEPROM at the beginning of the
auto-boot sequence.
1.1 Further Explanation of the Auto-Boot
Sequence
The auto-boot sequence is terminated by writing a
‘1’ to the STOP bit in the CS5460A’s Control Reg-
ister. This action is performed as the last command
in the EEPROM command sequence. At the com-
pletion of the write to the Control Register (provid-
ed STOP bit = “1”), SCLK stops, and CS rises,
thereby reducing power consumed by the EE-
PROM. At completion of the Auto-Boot sequence,
the serial port will revert to functioning as a slave-
mode
interface. Therefore, if desired, the
CS5460A registers can still be read by an external
device, such as a central office controller, connect-
ed to the meter assembly by a bus interface.
1.2 Sample Auto-Boot Sequence
The serial data for such a sample sequence is
shown below in single-byte hexidecimal notation:
40 00 00 61 ;In Configuration Register,
turn high-pass filters on, set
K = 1.
44 7F C4 A9 ;Write value of 0x7FC4A9 to
Current Channel Gain Regis-
ter.
46 7F B2 53 ;Write value of 0x7FB253 to
Voltage Channel DC Offset
Register.
4C 00 00 14 ;Set Pulse Rate Register to
0.625 Hz.
74 00 00 04 ;Unmask bit #2 (“LSD” bit in
the Mask Register).
E8 ;Start performing continuous
computation cycles.
78 00 01 40 ;Write STOP bit to Control
Register, to terminate auto-
boot initialization sequence,
and also set the EOUT pulse
output to Mechanical Counter
Format.
When the CS5460A is commanded by the EE-
PROM to perform a certain operation, the opera-
tion will not be pre-maturely terminated by the
assertion of the Control Register’s STOP bit. In the
above example, the ‘Start Conversions’ command
(0xE8) is issued from the EEPROM, and therefore
the CS5460A will continue to perform continuous
A/D conversions even after the STOP bit is asserted.
1.3 How do I reset the CS5460A in Auto-Boot
Mode during Brown-Out/Black-Out
conditions?
The power line that is to be metered may enter a
black-out or brown-out condition at certain times,
due to problems at the power plant or other envi-
ronmental conditions
(ground fault, electrical
storms, etc.) In such conditions, it is important for
the meter assembly to accomplish a proper reset,
FEB ‘03
AN225REV1