NEC uPD72257, Preliminary User'S Manual

Page: 100 / 343

4.7 System Controller Registers
4.7.1 System Controller registers overview
The System Controller is controlled and operated by means of the following
registers:
Table 4-4 System Controller registers overview
Register function Name Address
PLL control register SYSPLLCTRL
<SysC_Base> + 00
H
Clock control register SYSCLKCTRL
<SysC_Base> + 04
H
Reset control register SYSRESET
<SysC_Base> + 08
H
Boot mode register SYSBOOTMODE <SysC_Base> + 0C
H
Revision register SYSREV
<SysC_Base> + 10
H
Pin multiplex control register SYSPINMUX
<SysC_Base> + 14
H
Video Input enable control register SYSVIEN
<SysC_Base> + 20
H
Video Output control register SYSVOCTRL
<SysC_Base> + 24
H
System Watchdog control register SYSWDCTRL
<SysC_Base> + 28
H
System control write protection register SYSPROTECT
<SysC_Base> + 2C
H
<SysC_Base> The <SysC_Base> base address of the registers are defined in the first section of
this chapter under the key word "Register base addresses".
4.7.2 System Controller registers write protection
Generally all System Controller registers are read only and hence are protected
against unintentional write accesses.
For unlocking the registers for write accesses the SYSPROTECT register has to
be written with the value 0000 00A5
H
prior writing to the register to be modified.
After that only one write access to the System Controller address range is allowed.
In other words, writing 0000 00A5
H
to SYSPROTECT deactivates the write
protection of the System Controller registers and the next access to the System
Controller address range (which would normally be the intended write access)
activates the write protect again.
Note that any read or write access to any System Controller register after
SYSPROTECT = 0000 00A5
H
enables the write protection again.
Chapter 4 System Controller
100
Preliminary User's Manual S19203EE1V3UM00