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    Minimal Z80 Board  -  Mario Prato - December 1997       
         for any information: E.mail mprato@iqsnet.it                            
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This is my Z80 board :

#	Cpu Z80 at 4MHz (U6)
#	Ram 32 Kbytes with battery backup (U8)
#	Rom 8  Kbytes (U7)
#	Clock generator(U2)
#	Address Decoder (U5)
#	8 bits Output Port (U4)
#	8 bits Input Port (U3)
#	5V Voltage Regulator (U1)

Power supply:

Power supply of the board can be any voltage between 7 to 25 Volt but better
is to stay below 15 V.
Voltage regulator U1 must be mounted on a heat radiator.

Memory map:

System ROM is located from address 0000h to 1FFFh (8K), RAM start from 8000h end
to FFFFh (32K).
The only I/O address is 001H from that you can read/write to external ports.


	+--------+--------+----------------+
	|  rom   |  n.u.  |     ram        |
	|        |        |                |
	+--------+--------+----------------+
      0000H    1FFFH    8000H            FFFFH



IO map:

00h  read  not used  (select signal on U5 pin 5 is free for future use)
00h  write not used  (select signal on U5 pin 4 is free for future use)
01h  read  input port
01h  write output port



Building the board:

You can mount all the components on a prototype board, but if you have 
enough experience with PCB, you can use the tracks I give you.
My PCB is a dual face with no passing through holes, so before the insertion of
the components, you need to connect the traces of the component side with 
the copper side.

Bill of components	                      12 GEN 1998 20:28:28     

 BT1                       lithium battery 3.6 Volt 
 C1,C2                     100uF 25V electrolytic         
 C3,C4,C5                  100nF polyester         
 C6                        100pF Ceramic        
 C7                        1uF 16V electrolytic           
 D2,D3,D4,D5               1n914 o 1n4148 small signal silicon diode        
 J1,J2                     strip-line connector 10 pin step 2.54mm (0.1 in)        
 J3                        connector 2 pin step 5mm (0.2 in)        
 R1                        10K  1/8W         
 R3                        330  1/8W         
 R4,R5                     1200 1/8W         
 R6                        220K 1/8W         
 U1                        uA7805 or LM7805 (in TO-220 on heat sink)
 U2                        74LS04  inverter      
 U3                        74LS244 buffer      
 U4                        74LS374 latch      
 U5                        74LS139 decoder      
 U6                        Z80A CPU (good is a CMOS version)          
 U7                        27C64 eprom 8k x 8     
 U8                        AT28C256 or 62256 ram 32k x 8     
 Y1                        Quartz crystal 4 MHz         

Very important:
Capacitors c3,c4,c5 are useful to decouple power supply rail, but due to the 
small space available on the board they maybe inserted on the copper side or on the I.C. sockets. Refer to the schematics.

If you don't want to use the battery backup feature:
don't mount R1 and D4. short D5 and D3.

A good idea is to mount a push button over the C7 to manualy activate the CPU RESET.