Z90251 Datasheet, PDF (18/97 Pages) Zilog, Inc. – eZVision 200 Television Controllers with OSD

Z90255 ROM and Z90251 OTP
32 KB Television Controller with OSD
10
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.
Z90259 In-Circuit
Emulator (ICEbox)
Z90259
Z90251
ZOSD Board
Develop
code on PC
Download Code to
Z90259 ICE chip
Program the
Z90251 OTP
Converts to
Video Display
Figure 4 Code Development Environment
Review Code
on TV Display
2 Memory Description
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.
2.1 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.
Note: _{Registers E0h-EFh are only accessed through a working-}
register and indirect addressing mode.
PS001301-0800