"The In Circuit Emulator (ICE) allows an Acorn system to
connect to a second micro-processor target system by way of its 6502 processor
socket. Once established this connection may be used to test hardware and to
evaluate software in the target system. The ICE will be most useful in the
development of new 6502 based products and in the test and repair of existing
equipment.
The ICE hardware is carried on a single Eurocard (100 x
160mm) which connects to the standard Acorn system bus. A 40-way flat ribbon
cable plugs on to the front of this card and provides connection to the 40-way
dual-in-line plug for the target processor socket. In operation the ICE
re-locates any two blocks in the target system to appear as blocks A and B in
the host system. The selection of the two blocks is achieved by writing to the
ICE control register which is a latch on the ICE card. After setting the control
register any read or write operations by the host system into its blocks A or B
are sent down the ICE cable into the target system. In this way the target
system hardware may be accessed for testing with the same bus timing as would
appear from its own processor. As the block selection is under software control
programs for testing the target hardware can dynamically relocate the ICE
allowing the whole of the target memory map to be tested.
When developing software in the host system for eventual
use in the target system it will be necessary to define the machine addresses as
those in blocks A or B. After proving the program these addresses must be
changed to their real values before blowing the program into Read Only Memory
and fitting it and the 6502 to the target system.
Also on the ICE card is a single byte register which may be
read by the host system.
The bits in this register indicate the state of various
pins around the 6502 socket in the target system including the +5 volt rail and
the 1MHz clock.