Z85C3008VSG Zilog, Z85C3008VSG Datasheet - Page 21

• Manufacturer Part Number: Z85C3008VSG
• Description: IC 8MHZ Z8500 CMOS SCC 44-PLCC
• Manufacturer: Zilog
• Series: SCCr

Specifications of Z85C3008VSG

• Processor Type: Z80
• Features: Error Detection and Multiprotocol Support
• Speed: 8MHz
• Voltage: 5V
• Mounting Type: Surface Mount
• Package / Case: 44-LCC (J-Lead)
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: 0 C
• Mounting Style: SMD/SMT
• Cpu Speed: 8MHz
• Digital Ic Case Style: LCC
• No. Of Pins: 44
• Supply Voltage Range: 5V
• Operating Temperature Range: 0°C To +70°C
• Svhc: No SVHC (18-Jun-2010)
• Base Number: 85
• Rohs Compliant: Yes
• Clock Frequency: 8MHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 269-3932; Z85C3008VSG

PS011705-0608
INTACK
Interrupt Pending (IP), Interrupt Under Service (IUS), and Interrupt Enable (IE). Opera-
tion of the IE bit is straight forward. If the IE bit is set for a given interrupt source, then
that source can request interrupts. The exception is when the MIE (Master Interrupt
Enable) bit in WR9 is reset and no interrupts can be requested. The IE bits are Write only.
The other two bits are related to the interrupt priority chain (see
cessor peripheral, the SCC can request an interrupt only when no higher priority device is
requesting one, that is, when IEI is High. If the device in question requests an interrupt, it
pulls down INT. The CPU responds with INTACK, and the interrupting device places the
vector on the data bus.
The SCC can also execute an interrupt acknowledge cycle through software. In some CPU
environments, it is difficult to create the INTACK signal with the necessary timing to
acknowledge interrupts and allow the nesting of interrupts. In these cases, the INTACK
signal can be created with a software command to the SCC.
In the SCC, the Interrupt Pending (IP) bit signals a need for interrupt servicing. When an
IP bit is 1 and the IEI input is High, the INT output is pulled Low, requesting an interrupt.
In the SCC, if the IE bit is not set by enabling interrupts, then the IP for that source is
never set. The IP bits are readable in RR3A.
The IUS bits signal that an interrupt request is being serviced. If an IUS is set, all interrupt
sources of lower priority in the SCC and external to the SCC are prevented from request-
ing interrupts.
The internal interrupt sources are inhibited by the state of the internal daisy chain, while
lower priority devices are inhibited by the IEO output of the SCC being pulled Low and
propagated to subsequent peripherals. An IUS bit is set during an Interrupt Acknowl-
edge cycle, if there are no higher priority devices requesting interrupts.
There are three types of interrupts:
D7–D0
•
•
INT
+5 V
Transmit
Receive
IEI D7–D0 INT INTACK IEO
Figure 8. SCC Interrupt Priority Schedule
Peripheral
IEI D7–D0 INT INTACK IEO
CMOS SCC Serial Communications Controller
Peripheral
IEI D7–D0 INT INTACK
Peripheral
Figure
Product Specification
Functional Description
+5 V
8). As a micropro-
17