Z90251 ZILOG [Zilog, Inc.], Z90251 Datasheet - Page 18

• Manufacturer Part Number: Z90251
• Description: eZVision 200 Television Controllers with OSD
• Manufacturer: ZILOG [Zilog, Inc.]

2
Memory Description
2.1
Note:
Figure 4
A total of 300 bytes of general purpose register memory is implemented in the
Z90255. These registers are composed of 236 registers from the standard
register file and 64 registers from the expanded register file.
Standard Register File
The Z90255 Standard Register File consists of two I/O port registers (02h and
03h), 236 general purpose registers (04h-EFh) and 15 (F1h-FFh) control and
status registers. Registers 00h, 01h, and F0h are reserved. Figure 5 is the
register file map. Instructions can access registers directly or indirectly with an 8-
bit address field. This also allows short 4-bit addressing using the Register
Pointer. In the 4-bit mode, the register file is divided into sixteen working register
groups. The upper nibble of the Register Pointer (FDh) addresses the starting
location of the active working-register group.
code on PC
Develop
The Z90251 requires ZilogÕs Z90259ZEM Emulator with its proprietary Zilog
Developmental Studio (ZDS) software for programming. To view how code
is working, the emulator uses a ZOSD board which connects directly to a
television screen. Refer to Figure 4.
Registers E0h-EFh are only accessed through a working-
register and indirect addressing mode.
Code Development Environment
Download Code to
Z90259 ICE chip
Emulator (ICEbox)
Z90259 In-Circuit
Program the
Z90251 OTP
Z90259
Z90251
32 KB Television Controller with OSD
Video Display
Converts to
ZOSD Board
Review Code
on TV Display
PS001301-0800
10