Specifications

Counter/Timers
FUNCTIONAL DESCRIPTION
The TCU is similar to the 8254 Programmable Interval Timer in that
the programmable registers are the same. Some restrictions apply to
the operating modes of individual counter/timers because they are
connected to the V40 internally and external control inputs are not
available. These restrictions are discussed below in an explanation of
individual operating modes. Figure 7-1 illustrates the major functional
blocks of the TCU. These functional blocks are discussed in the
following paragraphs.
ReadWrite Control
IORD IOWR A1 A2 EN
Mode Register
High
Byte
Low
Byte
Count
Register
High
Byte
Low
Byte
Count
Latch
Status
Latch
Status
Register
16-Bit Down Counter
Control Logic
Clock Select and Divisor
Counter/
Timer 1
Counter/
Timer 0
TCLK
(Connector J3)
V40 CLOCK
(Internal)
Counter/ Timer 2
CLK CLK
CLK
TCTL2
(Connector J3)
TOUT0
(ICU)
TOUT1
(ICU, SCU )
TOUT2
(Connector J3)
Internal Data Bus
Figure 7–1. Counter/Timer Block Diagram.
Read/Write Contr
ol
This functional block monitors I/O control and address signals to
select programmable registers and control data flow.
7-4