Technical data

2-30 Diagnostic Procedures
2.5.1.12 IP21 LEDs Show a Static 0x12 Pattern
System is stuck in bootmaster arbitration. Diagnose per Section 2.5.1.11, “IP19 LEDs Show
a Static 0xc Pattern.”
2.5.1.13 LEDs Boot to Master/Slave Patterns but UART Output is Garbled or
Missing.
1. Check UART cable and connections.
2. Verify that the serial clock is matched to the UART speed. When connecting to the
UART, match the speed with the System Controller speed.
Note: The standard System Controller produces a 9600 baud clock.
2.5.2 IO4 Troubleshooting Procedures
If an IO4 failure occurs during the boot process, the error message will continue to scroll
across the System Controller display until the system is powered off. Clear the display by
first turning the key switch to the Manager position. Enter the Debug Settings menu and
set the Manu-Mode bit. Setting this bit sends the IP19 and IP21 PROM error messages to
the external UART on the System Controller (see Section 2.5.3, “Using the System
Controller”).
2.5.3 Using the System Controller
This section contains various troubleshooting procedures using the System Controller.
2.5.3.1 Systems With Dead Monitors or Terminals
This section shows how to connect an ASCII terminal to a system with a faulty IO4 board,
bad monitor, or bad terminal.
The workaround is based on the System Controller’s connection to all of the CC chips on
the lowest-numbered CPU board, over the polled serial bus. The polled serial bus is
composed of six address lines and two data lines, and is used primarily during the
bootmaster arbitration process. The System Controller can address all of the processors
through their respective CC chips, but only the bootmaster CPU is capable of responding.
A port (or UART) is tied directly to the System Controller. You can attach a terminal to this
port and use it to reach the CPU board by going through the controller and over the polled
serial bus. On rack-mounted systems, the System Controller UART is located in the lower
left corner of the midplane (when facing the front of the chassis). Deskside systems have
the UART located in the lower right corner of the backplane (when facing the rear of the
chassis). The port is labeled External Controller Serial on all systems.
Note: The System Controller UART is equipped with a permanently attached cable with
a DB-25 connector at the terminal end.