Z84C2008PEG Zilog, Z84C2008PEG Datasheet - Page 43

• Manufacturer Part Number: Z84C2008PEG
• Description: IC 8MHZ Z80 CMOS PIO 40-DIP
• Manufacturer: Zilog
• Series: Z80r

Specifications of Z84C2008PEG

• Processor Type: Z80
• Features: Low Power CMOS
• Speed: 8MHz
• Voltage: 5V
• Mounting Type: Through Hole
• Package / Case: 40-DIP (0.620", 15.75mm)
• Cpu Speed: 8MHz
• Digital Ic Case Style: DIP
• No. Of Pins: 40
• Supply Voltage Range: 5V
• Operating Temperature Range: -40°C To +100°C
• Svhc: No SVHC (18-Jun-2010)
• Rohs Compliant: Yes
• Processor Series: Z84C2xx
• Core: Z80
• Data Bus Width: 8 bit
• Maximum Clock Frequency: 8 MHz
• Number Of Programmable I/os: 16
• Operating Supply Voltage: 0 V to 5 V
• Maximum Operating Temperature: + 100 C
• Mounting Style: Through Hole
• Minimum Operating Temperature: - 40 C
• Base Number: 84
• Clock Frequency: 8MHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

UM008005-0205
Action
CPU Reset
A CPU reset forces both the IFF1 and IFF2 to the reset state, which disables
interrupts. Interrupts can be enabled at any time by an EI instruction from
the programmer. When an EI instruction is executed, any pending interrupt
request is not accepted until after the instruction following EI is executed.
This single instruction delay is necessary when the next instruction is a
return instruction. Interrupts are not allowed until a return is completed. The
EI instruction sets both IFF1 and IFF2 to the enable state. When the CPU
accepts a maskable interrupt, both IFF1 and IFF2 are automatically reset,
inhibiting further interrupts until the programmer issues a new El
instruction. Note that for all of the previous cases, IFF1 and IFF2 are always
equal.
The purpose of IFF2 is to save the status of IFF1 when a non-maskable
interrupt occurs. When a non-maskable interrupt is accepted, IFF1 resets to
prevent further interrupts until reenabled by the programmer. Thus, after a
non-maskable interrupt is accepted, maskable interrupts are disabled but the
previous state of IFF1 has been saved so that the complete state of the CPU
just prior to the non-maskable interrupt can be restored at any time. When a
Load Register A with Register I
Register A with Register R
of IFF2 is copied to the parity flag where it can be tested or stored.
A second method of restoring the status of IFF1 is through the execution of
a
instruction indicates that the non-maskable interrupt service routine is
complete and the contents of IFF2 are now copied back into IFF1 so that the
status of IFF1 just prior to the acceptance of the non-maskable interrupt is
restored automatically.
Table 2 is a summary of the effect of different instructions on the two enable
flip-flops.
Table 2. Interrupt Enable/Disable, Flip-Flops
Return From Non
-
Maskable Interrupt
IFF1 IFF2 Comments
0
0
(
LD A
,
Maskable Interrupt, INT Disabled
(
R
LD A
) instruction is executed, the state
,
I
(RETN) instruction. This
) instruction or a
User’s Manual
Z80 CPU
Load
Overview
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