In-System Debugging—IP2022 User’s Manual 334 www.ubicom.com 5.3 ISD/ISP Commands The ISD/ISP interface has two states, open and closed. Before
any commands are accepted, the interface must be opened with
the OPEN command. When the interface is closed, the IP2022
does not respond to any other commands. The CLOSE command
can     be     used     during     testing     to     make     sure     that     the
debugger/programmer is not interfering with the operation of the
target system.  OPEN  and  CLOSE  commands  are also  used to
connect   and   disconnect   the   debugger/programmer   while   the
target  system  is  running.  The  ISD/ISP  connector  may  only  be
attached  or  removed  while  the  ISD/ISP  interface  is  closed,  to
ensure that no spurious commands are issued to the IP2022. After  being  opened,  a  blank  device  must  be  initialized  with  the
INITIALIZE   command.   This   selects   various   modes   normally
specified in the FUSE0 register, including critical operating modes
such as clock source selection and the prescaler and postscaler
clock divisors. The OSC clock must be running before using the
debugging   or   programming   features,   however   the   SPI   clock
(TSCK) is the only clock required to be operational before issuing
the  INITIALIZE  command.  The  operand  word  issued  with  the
INITIALIZE command has the same format as the FUSE0 register.
The operand word is loaded into a temporary register that controls
the IP2022 until it is reset, as shown in Figure 5-2.