ST92196A datasheet(111/268 Pages) STMICROELECTRONICS

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- OSDRAM CONTROLLER

8.4 OSDRAM CONTROLLER

8.4.1 Introduction

The OSDRAM Controller handles the interface be-

tween the Display Controller, the CPU and the OS-

DRAM.

The time slots are allocated to each unit in order to

optimize the response time.

The main features of the OSDRAM Controller are

the following:

Memory mapped in Memory Space (segment

22h of the MMU)

DMA access for Display control

Direct CPU access

8.4.2 Functional Description

The OSDRAM controller manages the data flows

between the different sub-units (display controller,

CPU) and the OSDRAM. A specific set of buses

(16-bit data, 9-bit addresses) is dedicated to these

data flows. The OSDRAM controller accesses

these buses in real time. The OSDRAM controller

has registers mapped in the ST9 register file.

As this OSDRAM controller has also to deal with

TV real time signals (On-Screen-Display), a spe-

cific controller manages all exchanges:

– Its timing generator uses the same frequency

generator as the Display (Pixel frequency multi-

plier),

– Its controller can work in two TV modes:

– Single mode: all time slots are dedicated to

the CPU.

– Shared mode: time slots are shared between

the CPU and the Display. The shared mode is

controlled by the Display controller.

– Its architecture gives priority to the TV real time

constraints: whenever there is access contention

between the CPU and the Display (shared

mode), the CPU is automatically forced in a

“wait” configuration until its request is served.

– Its controller enables a third operating mode

(stand-alone mode) which allows the application

to access the OSDRAM while the Display is

turned off. In this case, the OSDRAM controller

uses the CPU main clock.

Figure 50. Display Architecture Overview

4 * 3 BITS

DISPLAY CONTROLLER

OSDRAM CONTROLLER

OSD DISPLAY RAM

CPU INTERFACE

ROM FONT

MATRIX

MEMORY BUSES

ADDRESS (6+4 BITS)

OSD ADDRESS (9 BITS)

OSD DATA

(16 BITS)

RGB

TRANSLUCENCY

TSLU

DATA (8 BITS)

ADDRESS (22 BITS)

DATA (8 BITS)

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