Technical Support Document number 72a 

Using the Epson HX-20 expansion unit


Refer to the 'Expansion Unit Mounting Procedure' booklet supplied 
with the unit for physical attachment to the HX-20. After mounting 
the unit you MUST cold start the machine by pressing CTRL @ the first 
time you use the machine. A cold start must also be carried out when 
the expansion unit is removed or the configuration changed. 

RAM and ROM options 

There are three basic configurations for the expansion unit as follows: 

 1)16k RAM + 18k ROM; with the expansion unit configured this 
way, the internal optional expansion ROM is disabled and cannot 
be used. This is particularly relevant to those users who wish 
to use the packages which contain the COMMS or RAX ROMS.
 2)8k RAM + 24k ROM; the internal optional expansion ROM is usable. 

 3)32k ROM; the internal optional expansion ROM is usable. 

In addition to being able to select the RAM/ROM combination for the 
expansion unit, you can also select the type of ROM which is used within 
the expansion unit. The types of ROM available for use are as follows: 

  SMM 2365 masked ROM 

  MBN 27C128 

Note: CMOS EPROMS should be used, otherwise battery life will be 
reduced from the normal 50 hours. 

Technical Support Document number 72a Setting the options The options described above are selected as follows: 1)RAM/ROM mixture: Option Switches Configuration 1 2 1 ON OFF 16k RAM + 16k ROM 2 OFF ON 8k RAM + 24k ROM (when using RAX or COMMS) 3 OFF OFF 32k ROM 2)ROM type: ROM type Switches Jumpers 3 4 1 2 27C64 OFF ON B B 27128 ON OFF A A Bank switching 07 When ROM is installed in both the main HX-20 and the expansion unit, it must be possible to switch between the banks of ROMS. This should only be carried out from machine code; the locations are as follows: $30 or $31 selects bank 1; the expansion unit ROMs $32 or $33 select bank 0; the HX-20 main ROMs