
10
56F805 Technical Data
2.5   Interrupt and Program Control Signals
Table 9.  Bus Control Signals
No. of 
Pins
Signal
Name
Signal
Type
State During 
Reset
Signal Description
1
PS
Output
Tri-stated
Program Memory Select
—PS is asserted low for external 
Program memory access.
1
DS
Output
Tri-stated
Data Memory Select
—DS is asserted low for external Data 
memory access. 
1
WR
Output
Tri-stated
Write Enable
—WR is asserted during external memory write 
cycles. When WR is asserted low, pins D0–D15 become 
outputs and the device puts data on the bus. When WR is 
deasserted high, the external data is latched inside the 
external device. When WR is asserted, it qualifies the A0–A15, 
PS, and DS pins. WR can be connected directly to the WE pin 
of a Static RAM.
1
RD
Output
Tri-stated
Read Enable
—RD is asserted during external memory read 
cycles. When RD is asserted low, pins D0–D15 become inputs 
and an external device is enabled onto the device’s data bus. 
When RD is deasserted high, the external data is latched 
inside the device. When RD is asserted, it qualifies the A0–
A15, PS, and DS pins. RD can be connected directly to the OE 
pin of a Static RAM or ROM. 
Table 10. Interrupt and Program Control Signals
No. of 
Pins
Signal 
Name
Signal
Type
State 
During
Reset
Signal Description
1
IRQA
Input
(Schmitt)
Input
External Interrupt Request A
—The IRQA input is a synchronized 
external interrupt request indicating an external device is requesting 
service. It can be programmed to be level-sensitive or negative-
edge-triggered.
1
IRQB
Input
(Schmitt)
Input
External Interrupt Request B
—The IRQB input is an external 
interrupt request indicating an external device is requesting service. 
It can be programmed to be level-sensitive or negative-edge-
triggered. 
1
RESET
Input
(Schmitt)
Input
Reset
—This input is a direct hardware reset on the processor. 
When RESET is asserted low, the device is initialized and placed in 
the Reset state. A Schmitt trigger input is used for noise immunity. 
When the RESET pin is deasserted, the initial chip operating mode 
is latched from the EXTBOOT pin. The internal reset signal will be 
deasserted synchronous with the internal clocks, after a fixed 
number of internal clocks.
To ensure complete hardware reset, RESET and TRST should be 
asserted together. The only exception occurs in a debugging 
environment when a hardware device reset is required and it is 
necessary not to reset the OnCE/JTAG module. In this case, assert 
RESET, but do not assert TRST.
F
Freescale Semiconductor, Inc.
For More Information On This Product,
  Go to: www.freescale.com
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