參數(shù)資料
型號(hào): C8254
廠商: Electronic Theatre Controls, Inc.
元件分類: 通用總線功能
英文描述: PROGRAMMABLE TIMER /COUNTER MEGAFUNCTION
中文描述: 可編程定時(shí)/計(jì)數(shù)器宏功能
文件頁數(shù): 4/6頁
文件大小: 290K
代理商: C8254
CAST C8254 Megafunction Datasheet
GATE#
Control
Logic
Upper/Lower
Byte
Controller
16-Bit Counter
CE16
16-Bit Output Latch
OLREG
MSB-CNTREG
CRM
LSB-CNTREG
CRL
8-Bit
Status
Register
CLK#
OUT#
Read
Counter
Controller
Control
Word
Upper/Lower
Byte
Controller
Read/Write
Control
Figure 2 – Internal Counter Block Diagram
Counter 0, Counter 1, Counter 2
These three functional blocks are identical in operation, so only a single Counter will be described. The
internal block diagram of a single counter is shown in Figure 2. The Counters are fully independent. Each
Counter may operate in a different Mode.
Control Logic
This block controls the 16-bit counter for all counting modes and the Null flag of the counter.
Upper/Lower Byte Controller
The width of the data bus is 8 bits, and the counter is 16 bits. The Upper/Lower Byte Controller allows one 8-
bit Counter Register, MSB or LSB, to be loaded one at a time from the internal bus. If the Counter is
programmed for two-byte read/write mode, this block will control which data byte will be read at the next
read cycle.
Counter Registers
There are two 8-bit registers called CRM and CRL. Both are normally referred to as one unit and called just
CR. When a new count is written to the Counter, the count is stored in the CR and later transferred to the
CE16. At the rising-edge of WRN, it will write data to the register. One register at a time will be allowed to be
loaded from the internal bus. After both registers have been loaded, both bytes are transferred to the CE16
simultaneously. CRM and CRL are cleared when the Counter is programmed.
Note that the CE16 can’t be written into; whenever a count is written, it is written into the CR.
CAST, Inc.
Page 4
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