HD64570 Datasheet, PDF (71/469 Pages) Hitachi Semiconductor – Serial Communications Adaptor

Section 3 System Controller
3.1 Overview
Features of the SCA's system controller:
• Three chip operating modes
Reset mode
Normal operating mode
System stop mode
• An on-chip bus arbiter arbitrates bus contention between the external bus master and on-chip
DMA controller
• Four 8- and 16-bit MPU bus interfaces can be switched under external control
3.2 Chip Operating Modes
3.2.1 SCA Operating Modes
The SCA supports three chip operating modes:
• Reset mode
• Normal operating mode
• System stop mode (low-power mode)
In reset mode, normal chip operations halt and registers are initialized. The chip enters reset mode
if a RESET signal is input during normal operating mode or system stop mode. Reset mode is
released when the RESET signal returns to the high level. The chip then enters normal operating
mode.
In normal operating mode, all on-chip functional modules operate at their normal performance
levels. From normal operating mode, transitions to either of the other operating modes are
possible.
System stop mode is a low-power mode in which all internal operations cease except for the clock
generator and reset circuits, to reduce power dissipation. From system stop mode, the SCA can
return to normal operating mode via reset mode, as shown in figure 3.1.
Rev. 0, 07/98, page 55 of 453