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Programmable Option Select (POS) eliminates the need for switches on the
system board by replacing their function with programmable registers. This
section describes the POS information that is used on the Server 95 system
board.
Warning! Programmable options should be set only
through the System Configuration utility programs. Directly setting the POS
registers or CMOS RAM POS parameters can result in multiple assignments of the
same system resource, improper operation of the feature, loss of data, or
damage to the hardware.
Note: Application programs should not use the
adapter identification (ID) unless absolutely necessary. Compatibility problems
can result.
The integrated I/O functions and memory on the system board use POS
information in three sets of POS registers: group 1 through group 3.
Group 1 POS Register
The diskette drive controller and parallel port B are configured through the
group 1 POS registers. These registers also contain the memory information that
identifies the type and size of memory installed.
Group 2 POS Register
The enable bit for all system board functions is in POS Register 2 of this
group. The serial ports are configured through group 2.
Group 3 POS Register
The high-speed parallel port (LPT A) is configured through group 3.
The following shows the register grouping, POS registers, and I/O functions
associated with the registers.
System Board Configuration Registers
| Group | POS
Register | Device |
|---|
| 1 | 2 | Floppy controller and parallel port B
(Disable system board function) |
| 1 | 3 | System board memory information |
| 1 | 4 | Diskette arbitration |
| 1 | 5 | Parallel port B arbitration |
| 2 | 2-4 | Serial port controller |
| 3 | 2-5 | High-speed parallel port |
System Board Enable/Setup Reg (Hex 0094) Put planar in setup mode
Adapter Enable/Setup Register (Hex 0096) Put card into setup mode
Operator Panel Registers (Hex 0108-010F) Write to op panel on a 95
Free Running Timer Command Reg (Hex 004B) Enable free run timer
Free Running Timer Count Regs (Hex 004C--004F) Access count
System Control Port B (Hex 0061) Mem. refresh, speaker, parity errors
RTC Address and NMI Mask Register (Hex 0070) Read/Write to RTC
RTC Data Register (Hex 0071) Read/write non-volatile memory in RTC
System Control Port C (Hex 007C) Enable Secure Media for EE floppies
Central Arbiter Register (Hex 0090) Access registers thru arbitration
Card Selected Feedback Register (Hex 0091) Monitor card status
System Control Port A (Hex 0092) Watchdog, security-lock, A20 etc
Group 1 POS Register 2 (Hex 0102) Controls FDC and LPT B
Group 1 POS Register 3 (Hex 0103) Info on planar memory connectors
Group 1 POS Register 4 (Hex 0104) Control diskette drive arbitration
Group 1 POS Register 5 (Hex 0105) Arbitration level for LPT B.
Group 2 POS Register 2 (Hex 0102) Configures planar serial ports
Group 2 POS Register 3 (Hex 0103) Address range serial ports
Group 2 POS Register 4 (Hex 0104) Version level of the serial chip
Group 3 POS Register 2 (Hex 0102) Configure high-speed parallel port
Group 3 POS Register 3 (Hex 0103) Reserved
Group 3 POS Register 4 (Hex 0104) Configure high-speed parallel port
Group 3 POS Register 5 (Hex 0105) Manage channel checks from LPT A
System Board Enable/Setup Register (Hex 0094)
This read-write register is used to place the system board functions into
setup mode and to select which group of registers is accessed during setup.
Configure only one group at a time.
Note: Ensure that all bits are set to 1 when not
performing setup on a system board function.
+----------------------------------------------+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|----+-----+-----------------------+-----+-----|
|GRP1| GRP2| Reserved | GRP3| R |
+----------------------------------------------+
GRP1: Enable/setup group 1
GRP2: Enable/setup group 2
GRP3: Enable/setup group 3
GRP1 When this bit is set to 0, the
diskette drive controller and parallel port B are placed in setup mode, and the
group 1 functions are accessed.
GRP2 When this bit is set to 0, the
system board serial ports are placed in setup mode, and the group 2 functions
are accessed.
GRP3 When this bit is set to 0, the
high-speed parallel port is placed in setup mode, and group 3 functions are
accessed.
Adapter Enable/Setup Register (Hex 0096)
This read/write register resets the channel, enables the respective '-card
setup' signal to configure adapters in the channel.
+-----------------------------------------------+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|-----+-----+-----+-----+-----+-----------------|
| RST | 0 | 0 | 0 | STUP| Select |
+-----------------------------------------------+
RST: Channel reset
SELECT: Channel select
STUP: Enable card setup
RST When this bit is set to 1, the
'channel reset' signal is activated to all connectors.
STUP The card-setup bit determines
whether the '-card setup' signal is driven active. This signal is used to put
an adapter into the setup mode. When this bit is set to 1, the signal is driven
active for the connector specified by the channel-select bits. When this bit is
set to 0, the signal is gated off.
SELECT The channel-select bits determine
which channel connector is put into the setup mode when the '-card setup'
signal is driven active. Connectors 1 through 8 are addressed as 0 through
7.
Note: -CD SETUP goes active only when the
microprocessor performs an I/O operation in the address range 0100h through
0107h.
Operator Panel Registers (Hex 0108-010F)
The Operator Panel has an eight-character
display that can be used to indicate operator messages and display system
status when the video display is turned off (in server environments, using the
display on the operator panel allows the video display to be turned off,
thereby reducing the power consumed).
The eight positions on the op-panel display are numbered right to left.
Operator Panel Position Numbering
Eight write-only registers provide a means of writing characters to each
position. Operator Panel Register 1 (address 0108h) defines the character in
position 1. Operator Panel Register 8 (address 010Fh) defines the character at
position 8.
The Character field can select one of 128 characters from 00 to 7Fh; bit 7
is reserved. The character codes 20h through 7Eh are the standard ASCII
characters.
Operator Panel Register
+-----------------------------------------------+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|-----+-----------------------------------------|
| R | Character |
+-----------------------------------------------+
For example, to write the number 307 in the display panel starting at
the left-most position:
- Write 33h to Operator Panel Register 8 (010Fh)
- Write 30h to Operator Panel Register 7 (010Eh)
- Write 37h to Operator Panel Register 6 (010Dh)
The 32-bit free-running timer has five 8-bit registers, a command register
and four count registers.
Free Running Timer Command Register (Hex 004B)
This read/write register is used to enable the free-running timer and to
command the timer to load the count (capture) specified in the Count Data
registers.
+-----------------------------------------------+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|-----------+-----+-----------------+-----+-----|
| Reserved | LD | Reserved | ENA | TST |
+-----------------------------------------------+
LD: Load count
ENA: Enable timer test
TST: Test mode
LD The load-count bit is a write-only
bit that is used to issue the capture command to the timer. Setting this bit to
1 causes the timer to load the value specified in the Count registers to the
internal counter. Setting this bit to 0 has no effect. This bit always reads as
a 1.
ENA The enable-timer-test bit controls
the timer while the timer is in the test mode. While this bit is set to 0 and
the timer is in the test mode, the input clock is disabled, and the count can
be loaded into the Count registers (004Ch through 004Fh). When the bit is set
to 1, the timer starts counting. When the timer is in the operating mode (the
test-mode bit is 1), the input clock is always enabled and operating and this
bit has no effect on the timer.
TST The test-mode bit controls the timer
state. When the bit is set to 1, the timer exits the test mode and is locked
into the operational mode. This bit is reset to 0 at power-on.
Free Running Timer Count Registers (Hex 004C--004F)
These four registers are used to access the count value in the internal
counter.
+-----------------------------------------------------+
| Count 31-24 | Count 23-16 | Count 15-8 | Count 7-0 |
+-----------------------------------------------------+
004Fh 004Eh 004Dh 004Ch
Count The Count field contains the
32-bit count of the free-running timer. The value is decreased by 1 for each
tick value. When the value reaches 0000h, the internal counter registers are
reloaded with the initial count value, and the counting continues.
System Control Port B (Hex 0061)
The following figure shows the bit definitions for read and write operations
to this port.
Read
+-----------------------------------------------+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|-----+-----+-----+-----+-----+-----+-----+-----|
| P | CHK | OT2 | REF | DCK | DP | SPK | GT2 |
+-----------------------------------------------+
Write
+-----------------------------------------------+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|-----+-----------------+-----+-----+-----+-----|
| RT0 | Reserved | DCK | DP | SPK | GT2 |
+-----------------------------------------------+
P: Parity check
RT0: Reset timer 0
CHK: Channel check
OT2: Timer 2 output
REF: Refresh request toggle
DCK: Disable channel check
DP: Disable parity check
SPK: Enable speaker data
GT2: Timer 2 gate to speaker
P The parity-check bit (bit 7) is a
read-only bit that indicates whether a parity error was detected. When the bit
is 1, a parity error was detected.
RT0 The reset-timer-0 bit is a
write-only bit that is used to reset the timer-tick interrupt (timer 0 output).
Setting this bit to 1 resets the output of timer 0 and IRQ0. Setting this bit
to 0 has no effect. (See the definition of the parity-check bit.)
CHK The channel-check bit (bit 6) is a
read-only bit that indicates if a channel-check condition has occurred. When
this bit is a 1, a channel-check condition has occurred.
OT2 The timer-2-output bit (bit 5) is a
read-only bit that reflects the state of the output from timer 2 (tone
generator).
REF The refresh-request bit (bit 4) is a
read-only bit that toggles for memory refresh request.
DCK The disable-channel-check bit is
used to enable and disable nonmaskable interrupts when a channel-check
condition is detected. When this bit is set to 0, channel checks are enabled.
It is set to 1 during POST and reset to 0 after POST has been completed.
DP The disable-parity-check bit (bit 2)
is used to enable and disable nonmaskable interrupts caused by parity errors.
When this bit is set to 0, parity checks are enabled. It is set to 1 during
POST and reset to 0 after POST has been completed.
SPK The enable-speaker-data bit (bit 1)
is used to enable and disable the output to the speaker. When this bit is set
to 1, speaker data is enabled.
GT2 The timer-2-gate bit (bit 0) is used
to enable and disable timer 2. When this bit is set to 1, the timer 2 is
enabled.
RTC Address and NMI Mask Register (Hex 0070)
This register is used with the RTC Data register (hex 0071) to read from and
write to the RT/CMOS RAM bytes.
Warning! The operation following a write operation
to this register must access the RT/CMOS Data register (hex 0071); otherwise,
intermittent malfunctions and unreliable operation of the RT/CMOS RAM can
occur.
+-----------------------------------------------+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|-----+-----------------------------------------|
| NMI | Address |
+-----------------------------------------------+
NMI: NMI mask
ADDRESS: RT/CMOS RAM address
NMI The NMI-mask bit is a read/write bit
that is used to enable and disable nonmaskable interrupts. Setting this bit to
1 disables (or masks) the NMI (see Nonmaskable Interrupt). Setting this bit to
0 enables the NMI. This bit is set to 1 during a power-on reset, but it is
reset to 0 before POST is completed.
Address The address field is a
write-only field that specifies the address within the RT/CMOS data area that
is accessed through the RT/CMOS Data register.
RTC Data Register (Hex 0071)
This register is used with the RTC Address and NMI Mask register to read
from and write to the nonvolatile RAM data area.
+-----------------------------------------------+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|-----------------------------------------------|
| RT/CMOS data |
+-----------------------------------------------+
System Control Port C (Hex 007C)
This read/write register is used to enable the secure media mode (see Secure
Media Mode).
Note: When writing to this register:
- Read the register to ensure that bit 7 is 0.
- Change only the enhanced-command bit.
- Write the new value to the register.
+-----------------------------------------------+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|-----+-----------------------------------+-----|
| TIP | Reserved | ENC |
+-----------------------------------------------+
TIP: Transfer in progress
ENC: Enhanced command/status
TIP The transfer-in-progress bit (bit 7)
is a read-only bit that indicates whether the EEPROM is in the process of
transferring data. While a transfer is in progress, this register is busy and
must not be modified.
When this bit is 1, the EEPROM is in the process of transferring data, and
the register is not available to be modified. When this bit is 0, a transfer is
not in progress, and the contents of register can be safely modified.
ENC The enhanced-command/status bit (bit
0) controls the state of the -security cmd signal to the diskette drive
connector. This signal is used to place the diskette drive in the secure media
mode in order to issue enhanced commands to the drive and to retrieve enhanced
status. The mode and commands require that both the drive and diskette drive
controller support this signal.
When the bit is set to 0, the -security cmd signal is driven active
low).
When the bit is set to 1, the signal is driven inactive (high).
Changing the -security cmd signal from active to inactive (bit 0 is reset to
1) issues an enhanced command to the selected drive.
Central Arbiter Register (Hex 0090)
The central-arbitration control-point (CACP) provides access to programmable
options through the Arbitration register, which is at I/O address hex 0090.
Read
+-----------------------------------------------+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|-----+-----+-----+-----+-----------------------|
| EPC | NMI | BTO | R | Arb Level |
+-----------------------------------------------+
Write
+-----------------------------------------------+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|-----+-----+-----------------------------------|
| EPC | MSK | Reserved |
+-----------------------------------------------+
EPC: Enable processor cycle
MSK: Arbitration mask
R: Reserved
NMI: NMI occurred
BTO: Bus time-out
EPC The enable-processor-cycle bit
controls whether the system CPU can use the channel while other devices are
arbitrating for control. When this bit is set to 1, the system microprocessor
can transfer data on the system bus while ARB/-GNT is in the ARB state.
This bit can be set to 0 if an arbitrating device requires total control of
the channel bandwidth. The power-on self-test (POST) sets this bit to 1.
MSK The arbitration-mask bit is a
write-only bit that enables and disables the CACP. Setting this bit to 1 causes
the CACP to enter the arbitration state, which forces ARB/-GNT to the ARB
state. The system CPU controls the channel until this bit is reset to 0 by a
system reset.
Warning! This bit should be set to 1 only by
diagnostic routines and system error-recovery routines.
NMI The NMI-occurred bit is a read-only
bit that indicates whether an NMI was detected. When an NMI occurs, the CACP is
forced into the arbitration state, which prevents any bus-masters from getting
control of the channel. Reading this register reset this bit to 0.
BTO The bus-time-out bit is a read-only
bit that indicates whether the NMI was caused by a bus timeout or some other
reason. If the bit is 1, the NMI was caused by a bus time-out. If the bit is 0,
the NMI is caused by another error. Reading this register resets this bit to
0.
EXT The enable-extended-arbitration bit
is a write-only bit that controls the minimum arbitration cycle. When this bit
is set to 0, the minimum arbitration cycle is 300 ns; setting this bit to 1
extends that minimum cycle to 600 ns. POST sets this bit to 0.
ARB The arbitration-level bits are
read-only bits that indicate the arbitration level of the arbiter that was
granted control of the channel during the most recent arbitration cycle. This
information allows the system CPU to determine the arbitration level of the
device that caused a bus time-out.
Card Selected Feedback Register (Hex 0091)
The Card Selected Feedback register is a read-only register at address hex
0091. It allows programs to monitor the '-card selected feedback' signal (-CD
SFBK). When an adapter is addressed, it responds by driving this signal active.
Diagnostic and configuration programs use this signal to verify the operation
of an adapter at a given address or DMA port.
+-----------------------------------------------+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|-----------------------------------------+-----|
| Reserved | SFB |
+-----------------------------------------------+
SFB: Card selected feedback
SFB When the card-selected-feedback bit
(bit 0) is 1, the -CD SFBK signal from an adapter in the channel was active on
a previous cycle or a system board I/O function (diskette drive, serial port,
or parallel port) was accessed by an I/O cycle. Reading this register resets
the bit to 0.
System Control Port A (Hex 0092)
Watchdog timer, security-lock, A20, hot reset.
+--------------------------------------------------------+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|--------------------+------+------+------+------+-------|
| Reserved | WD | SEC | R | A20 | ARS |
+--------------------------------------------------------+
WD: Watchdog-timer status
SEC: Security lock
R: Reserved
A20: Alternate gate A20
ARS: Alternate hot reset
WD The watchdog-timer-status bit (bit 4)
is a read-only bit that indicates the status of the watchdog timer. When this
bit is 1, a watchdog time-out has occurred. For more information about the
watchdog timer, refer to Programmable Timers in the IBM Personal System/2
Hardware Interface Technical Reference--Common Interfaces.
SEC The security-lock bit (bit 3)
provides the security lock for the secured area of RT/CMOS RAM that hold the
power-on password. When this bit is set to 1, the 8-byte password is
electronically locked. POST sets this bit; it can be cleared only by turning
the system off.
A20 The gate-A20 bit (bit 1) is ORed
with bit 1 in the Keyboard Output port to enable the 'address 20' line (A20).
When both bits are set to 0, A20 is disabled and is always 0. This bit is set
to 0 during POST.
ARS The alternate-hot-reset bit (bit 0)
provides an alternative method of resetting the system microprocessor.
Resetting the system microprocessor switches the microprocessor from protected
mode to real-address mode. The alternative reset takes 13.4 ms.
This bit is set to 0 by either a system reset or a write operation. When a
write operation changes this bit from 0 to 1, the alternative reset pin is
pulsed high for 100 to 125 ns. The reset occurs after a minimum delay of 6.72
us. While the reset is occurring, the latch remains set so that POST can read
the state of this bit. If this bit is 1, POST assumes that the microprocessor
is being switched from protected mode to real mode.
When using this bit to reset the system microprocessor to real mode, use the
following procedure:
- Disable all maskable and nonmaskable interrupts.
- Reset the system microprocessor by setting the bit to 1.
- Issue a Halt instruction to the system microprocessor.
- Reenable all maskable and nonmaskable interrupts.
Note: Whenever possible, use advanced BIOS (ABIOS)
to reset the system to real mode.
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