Datasheet

Data Sheet AD9558
Rev. B | Page 43 of 104
WATCHDOG TIMER
The watchdog timer is a general purpose programmable timer.
To set the timeout period, the user writes to the 16-bit watchdog
timer register (Address 0x0210 to Address 0x0211). A value of
0b in this register disables the timer. A nonzero value sets the
timeout period in milliseconds (ms), giving the watchdog timer
a range of 1 ms to 65.535 sec. The relative accuracy of the timer
is approximately 0.1% with an uncertainty of 0.5 ms.
If enabled, the timer runs continuously and generates a timeout
event when the timeout period expires. The user has access to
the watchdog timer status via the IRQ mechanism and the
multifunction pins (M7 to M0). In the case of the multifunction
pins, the timeout event of the watchdog timer is a pulse that lasts
32 system clock periods.
There are two ways to reset the watchdog timer (thereby
preventing it from causing a timeout event). The first is by
writing a Logic 1 to the autoclearing clear watchdog bit in the
reset functions register (Register 0x0A03, Bit 0). Alternatively,
the user can program any of the multifunction pins to reset the
watchdog timer. This allows the user to reset the timer by means
of a hardware pin rather than by using a serial I/O port operation.
EEPROM
EEPROM Overview
The AD9558 contains an integrated 2048-byte, electrically
erasable, programmable read-only memory (EEPROM).
The AD9558 can be configured to perform a download at
power-up via the multifunction pins (M3 and M2), but uploads
and downloads can also be done on demand via the EEPROM
control registers (Address 0x0E00 to Address 0x0E03).
The EEPROM provides the ability to upload and download
configuration settings to and from the register map. Figure 44
shows a functional diagram of the EEPROM.
Register 0x0E10 to Register 0x0E3F represent a 53-byte EEPROM
storage sequence area (referred to as the “scratch pad” in this
section) that enables the user to store a sequence of instructions
for transferring data to the EEPROM from the device settings
portion of the register map. Note that the default values for
these registers provide a sample sequence for saving/retrieving
all of the AD9558 EEPROM-accessible registers. Figure 44 shows
the connectivity between the EEPROM and the controller that
manages data transfer between the EEPROM and the register map.
The controller oversees the process of transferring EEPROM data
to and from the register map. There are two modes of operation
handled by the controller: saving data to the EEPROM (upload
mode) or retrieving data from the EEPROM (download mode).
In either case, the controller relies on a specific instruction set.
EEPROM
(0x000
T
O 0x1FF)
DATA
DATA
DATA
EEPROM
ADDRESS
POINTER
M3
M2
REGISTER MAP
DEVICE
SETTINGS
(0x0004 T
O 0x0A0D)
SCRATCH PAD
(EEPROM STORAGE SEQUENCE)
(0x0E10 TO 0x0E45)
SERIA
L
INPUT/OUTPUT
PORT
CONDITION
(0E01 [3:0])
SCR
ATC
H PA
D
ADD
RESS
P
OIN
TER
DEVICE
SETTINGS
ADDRESS
POINTER
EEPROM
CONTROLLER
09758-024
Figure 44. EEPROM Functional Diagram