HD64570 HITACHI [Hitachi Semiconductor], HD64570 Datasheet - Page 52

• Manufacturer Part Number: HD64570
• Description: Serial Communications Adaptor
• Manufacturer: HITACHI [Hitachi Semiconductor]

1.7.13
Interrupt Control
SCA interrupts are controlled by three interrupt status registers (ISR0, ISR1, ISR2) containing
flags for 20 interrupt sources, three interrupt enable registers (IER0, IER1, IER2) which can mask
the interrupt source flags individually, and one interrupt control register (ITCR) (figure 1.24).
The interrupt sources are located in corresponding functional modules (MSCI, DMAC, timers).
When an interrupt source that is not masked becomes active, the SCA activates INT to request an
MPU interrupt. When the MPU activates INTA in response, the SCA begins an acknowledge
cycle and outputs an interrupt vector according to register settings.
The interrupt control register (ITCR) selects the interrupt priority order, the type of acknowledge
cycle, and the type of vector output. ITCR bits IAK0 and IAK1 select the non-acknowledge, single
acknowledge, or double acknowledge cycle. Nonacknowledge means that the SCA does not output
an interrupt vector when INTA is activated. Single acknowledge means that the SCA outputs a
vector the first time INTA is activated. Double acknowledge means that the SCA outputs a vector
the second time INTA is activated.
ITCR bit VOS selects whether to output the contents of the interrupt vector register (IVR) or
interrupt modified vector register (IMVR) as the vector. Any value can be set in IVR for
unmodified output as the vector in the acknowledge cycle. The highest two bits of IMVR can be
set to any value, but the lower six bits hold a hardware-generated code representing the interrupt
source. If multiple interrupt sources are active simultaneously, IMVR holds the code of the source
with the highest priority. ITCR bit IPC can switch the relative priority of the MSCI and DMAC.
See figures 1.25 to 1.27 for interrupt logic flow for MSCI, DMAC, and timer modules.
Rev. 0, 07/98, page 36 of 453