ST90158 - DEVICE ARCHITECTURE
2.3 SYSTEM REGISTERS
The System registers are listed in Table 4. They
are used to perform all the important system set-
tings. Their purpose is described in the following
pages. Refer to the chapter dealing with I/O for a
description of the PORT[5:0] Data registers.
Table 4. System Registers (Group E)
PAGE POINTER REGISTER
REGISTER POINTER 1
REGISTER POINTER 0
CENTRAL INT. CNTL REG
PORT5 DATA REG.
PORT4 DATA REG.
PORT3 DATA REG.
PORT2 DATA REG.
PORT1 DATA REG.
PORT0 DATA REG.
2.3.1 Central Interrupt Control Register
Please refer to the ”INTERRUPT” chapter for a de-
tailed description of the ST9 interrupt philosophy.
CENTRAL INTERRUPT CONTROL REGISTER
R230 - Read/Write
Register Group: E (System)
Reset Value: 1000 0111 (87h)
IAM CPL2 CPL1 CPL0
Bit 7 = GCEN: Global Counter Enable.
This bit is the Global Counter Enable of the Multi-
function Timers. The GCEN bit is ANDed with the
CE bit in the TCR Register (only in devices featur-
ing the MFT Multifunction Timer) in order to enable
the Timers when both bits are set. This bit is set af-
ter the Reset cycle.
Note: If an MFT is not included in the ST9 device,
then this bit has no effect.
Bit 6 = TLIP: Top Level Interrupt Pending.
This bit is set by hardware when a Top Level Inter-
rupt Request is recognized. This bit can also be
set by software to simulate a Top Level Interrupt
0: No Top Level Interrupt pending
1: Top Level Interrupt pending
Bit 5 = TLI: Top Level Interrupt bit.
0: Top Level Interrupt is acknowledged depending
on the TLNM bit in the NICR Register.
1: Top Level Interrupt is acknowledged depending
on the IEN and TLNM bits in the NICR Register
(described in the Interrupt chapter).
Bit 4 = IEN: Interrupt Enable .
This bit is cleared by interrupt acknowledgement,
and set by interrupt return (iret). IEN is modified
implicitly by iret, ei and di instructions or by an
interrupt acknowledge cycle. It can also be explic-
itly written by the user, but only when no interrupt
is pending. Therefore, the user should execute a
di instruction (or guarantee by other means that
no interrupt request can arrive) before any write
operation to the CICR register.
0: Disable all interrupts except Top Level Interrupt.
1: Enable Interrupts
Bit 3 = IAM: Interrupt Arbitration Mode.
This bit is set and cleared by software to select the
0: Concurrent Mode
1: Nested Mode.
Bit 2:0 = CPL[2:0]: Current Priority Level.
These three bits record the priority level of the rou-
tine currently running (i.e. the Current Priority Lev-
el, CPL). The highest priority level is represented
by 000, and the lowest by 111. The CPL bits can
be set by hardware or software and provide the
reference according to which subsequent inter-
rupts are either left pending or are allowed to inter-
rupt the current interrupt service routine. When the
current interrupt is replaced by one of a higher pri-
ority, the current priority value is automatically
stored until required in the NICR register.