Z84C90_12 Datasheet, PDF (14/56 Pages) Zilog, Inc. – KIO Serial/Parallel Counter/Timer

Z84C90 KIO Serial/Parallel Counter/Timer
Product Specification
7
Clock Oscillator/Driver Logic Unit. A clock oscillator/driver is available that will allow
the user to eliminate circuitry with in a new design, or that can be used as another oscilla-
tor within the system. This logic will accept either a crystal ceramic resonator or TTL-
compatible clock input and generate a MOS-compatible clock output and also an oscillator
reference output. Zilog recommends a fundamental parallel resonant crystal; see Figure 6.
The preferred value of the two capacitors C1 and C2 is 33 pF each.
C1
ZTALI
Crystal
Inputs
C2
XTALO
Figure 6. Crystal Connection
Command Logic Unit. This logic unit provides for much more than just controlling the
interface between the KIO and the CPU. The main function provided by this unit is to
allow the user to configure the internal interrupt daisy chain of the KIO into a preferred
sequence of peripherals to interrupt. Any one of the three devices (SIO, CTC, PIO) can be
the highest priority, while another can be second priority and the remaining device the
third. The user can even configure the daisy chain such that no internal peripherals are
involved in the chain. Programming of the daisy chain configuration is performed by pro-
gramming the Command Register with the appropriate 3-bit pattern in addresses D0–D2,
with D3 set to 1.
A second function of this logic unit is to provide software-controllable hardware resets to
each of the individual devices. As a result, an individual peripheral is allowed to be reset
without having to reset the entire KIO. Requiring bit D3 to be set to a 1 to program the
daisy chain configuration allows the user to reset the individual devices without changing
the daisy chain. The software reset commands for the individual devices still remain avail-
able to the user.
A third function of the Command Register allows the user to obtain use of the additional
control signals of the SIO logic instead of the PIA port by programming bit D7 of the
Command Register with a 1.
PS011804-0612
Block Descriptions