Cirrus Logic EP93xx - Manual (Page 128)

5-2 DS785UM1
Copyright 2007 Cirrus Logic
System Controller
EP93xx User’s Guide
5
5
5
certain system variables such as RTC, SDRAM refresh control/global configuration, and
the Syscon registers.
Note: If PLLs are enabled, user reset does NOT disable or reset the PLLs. They retain their
frequency settings.
• Three-key reset. When F2, F4, and F7 are pressed, a user reset occurs.
• Software reset and watchdog reset. They perform the functions of the user reset, but are
under software control.
“Watchdog” on page 19-3 and “PwrSts” on page 5-14 registers contain the information
regarding which reset event occurred. Note that only the Watchdog timer contains
information about a user-generated 3-key reset.
5.1.3 Hardware Configuration Control
The Hardware Configuration controls provide a mechanism to place the system into various
boot configurations. In addition, one of several external boot memory options can be selected
at system wake up.
The Hardware Configuration controls are defined by a set of device pins that are latched into
configuration control bits on the rising edge of the PRSTn or RSTOn pin. The different
hardware configuration bits define watchdog behavior, boot mode (internal or external), boot
synchronicity, and external boot width. The latched pins are described in
Table 5-1 .
The latched version of these signals have an “L” prefix, are stored in the SysCfg register, and
are readable by software. Note that the signals EECLK and EEDAT may have 1 k
Ω
pull-up
resisters if used in an open-drain two-wire serial port application. (The default state
assignments will assume these pull-ups.)
The Hardware Control configurations are show in Table 5-2 .
Table 5-1. Hardware Configuration Control Latched Pins
Pin Name(s) Action
CSn[1]
Enable/Disable Watchdog
reset timer
CSn[2]
Enable/Disable Watchdog
reset duration
CSn[3] Should be pulled-up to “1”
EECLK
Select internal or external
boot
EEDAT Should be pulled-up to “1”
BOOT[1:0] Select boot mode
ASDO
Select synchronous or
asynchronous boot
CSn[7:6] Select external boot width