Service manual

Service Manual
*PMonitor
Display the text normally written to the LCD.
Syntax
*PMonitor
Use
This command may be used to simulate a display
adapter using the external test interface. If no output
appears from the target within a short time, and the
target is not ready to receive a command from the
test interface, it is reset. If the target is ready to
receive a command, it is sent the command normally
generated by the display adapter. This should start
the self-test.
When the self-test sequence is completed, the target
will display the test result on screen and disc LED as
described in the display adapter section above. The
target will not accept further commands until it is
reset.
The Monitor operation will continue indefinitely unless
halted with the Esc key.
Example
*PMonitor
Related commands
*PReset
Display/debug interface
The display/debug interface connects to machines with
an external test connector through a 0.025 in sq 0.1 inch
pitch 6-way plug. This has connections as follows:
1 +5v
2 D<0> 2K2 pull-up to +5v on interface
3 LA<21> Output pulse to interface
4 ROMCS* Response connection from interface
5 RST* Open-collector drive to Reset
6 0v
You can use the interface with earlier Archimedes
systems by making appropriate temporary connections.
Do this using a 0.025 in sq 0.1 inch pitch 3-way plug to
connect +5v, 0v and RST to pins 17, 16 and 15
respectively of the Econet interface connector. Use
miniature test clips (E-Z hooks) or an IC clip to pick up
ROMCS and D<0> from one of the ROM sites (D<0>
need not be used – any data line will do) and LA<21>
from the address latches (IC30 pin 19 on an A3000).
300-series and early 400 series machines drive ROMCS
directly from a PAL and this signal cannot be safely
overdriven. To overcome this, place a 330R resistor in
the signal from the PAL, as follows:
1 Stack two 20-pin sockets on top of one another,
bending pin 18 out so that the connection is not
carried right through the stack.
2 Solder a 330R resistor in line, so that when the
adapter is used to hold the PAL, pin 18 is connected
through the resistor rather than directly.
3 Remove the PAL from its socket near MEMC, insert
the adapter in the PAL socket and fit the PAL in
adapter socket.
The display/debug interface is primarily a serial-to-
parallel interface with some additional features for
synchronization and bidirectional data transfer. A shift
register is used to perform the serial to parallel
conversion, with a 22V10 PAL to perform control and
decoding functions. The serial protocol is encoded using
groups of pulses closer together than 4µS or spaced
apart by more than 164. Discrimination is performed by
a retriggerable monostable with a period near 104.
The pulses are transmitted by the target using the LA21
address line. This line is a 'don't care' in ROM address
space, and accesses to a ROM address with this line
asserted will normally return data from an aliased ROM
address. The interface may respond to the LA21 pulse
by forcing ROMCS inactive for the duration of the data
fetch: the integral test software will then read the bus
with no ROM driving it, obtaining a result different from
that read from the aliased ROM address. A pull-up on
one bit of the data bus ensures that the value read when
nothing drives the bus is non-zero. The integral test
software actually asserts both A22 and A21 for the test
operation: this allows for expansion to 4MB of ROM.
A number of pulse sequences are recognised by the
interface hardware:
5-14 Issue 2, June 1991 Part 5 - Main PCB fault diagnosis