LOGXMAS25.BIN

Author:   Logon System
Category: Christmas Challenge
System:   Amstrad CPC
Language: Z80 Assembly (using CPC Firmware)
Len source code: 1191 bytes
Len exe file:     25 bytes
Len code only:    25 bytes

Instructions:
Insert logxmas25.dsk
Type:
      memory&1340:load"logxmas":cls:call&1341

Description:
First trick is about z80 registers which are preloaded and fixed
when an executable is launched by a genuine RUN"program.bin
Second trick is about system call to locate x,y on text screen :
input registers H and L are updated (decremented -1) at output

Comments:
This is a coop work ! and we did it ! :D Working together is the key. 
We got a better result than in our 2 own personal challenges.