
56F807 Technical Data Technical Data, Rev. 15
12
 Freescale Semiconductor
2.5   Interrupt and Program Control Signals
Table 2-7 Data Bus Signals
No. of 
Pins
Signal
Name
Signal 
Type
State During 
Reset
Signal Description
16
D0–D15
Input/O
utput
Tri-stated
Data Bus
— D0–D15 specify the data for external program or data 
memory accesses. D0–D15 are tri-stated when the external bus is 
inactive. Internal pullups may be active.
Table 2-8  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 2-9 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 that indicates that 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 that indicates that an external device is requesting 
service. It can be programmed to be level-sensitive or 
negative-edge-triggered.