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CS82C88 Datasheet(PDF) 3 Page - Renesas Technology Corp |
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CS82C88 Datasheet(HTML) 3 Page - Renesas Technology Corp |
3 / 12 page 82C88 FN2979 Rev 3.00 Page 3 of 12 August 13, 2015 Functional Description The command logic decodes the three 80C86, 8086, 80C88, 8088, 80186, 80188 or 8089 status lines (S0, S1, S2) to determine what command is to be issued (see Table 1). I/O Bus Mode The 82C88 is in the I/O Bus mode if the IOB pin is strapped HIGH. In the I/O Bus mode, all I/O command lines IORC, IOWC, AIOWC, INTA) are always enabled (i.e., not dependent on AEN). When an I/O command is initiated by the processor, the 82C88 immediately activates the command lines using PDEN and DT/R to control the I/O bus transceiver. The I/O command lines should not be used to control the system bus in this configuration because no arbitration is present. This mode allows one 82C88 Bus Controller to handle two external busses. No waiting is involved when the CPU wants to gain access to the I/O bus. Normal memory access requires a “Bus Ready” signal (AEN LOW) before it will proceed. It is advantageous to use the IOB mode if I/O or peripherals dedicated to one processor exist in a multi-processor system. System Bus Mode The 82C88 is in the System Bus mode if the IOB pin is strapped LOW. In this mode, no command is issued until a specified time period after the AEN line is activated (LOW). This mode assumes bus arbitration logic will inform the bus controller (on the AEN line) when the bus is free for use. Both memory and I/O commands wait for bus arbitration. This mode is used when only one bus exists. Here, both I/O and memory are shared by more than one processor. Command Outputs The advanced write commands are made available to initiate write procedures early in the machine cycle. This signal can be used to prevent the processor from entering an unnecessary wait state. INTA (Interrupt Acknowledge) acts as an I/O read during an interrupt cycle. Its purpose is to inform an interrupting device that its interrupt is being acknowledged and that it should place vectoring information onto the data bus. The command outputs are: MRDC - Memory Read Command MWTC - Memory Write Command IORC - I/O Read Command IOWC - I/O Write Command AMWC - Advanced Memory Write Command AIOWC - Advanced I/O Write Command INTA - Interrupt Acknowledge Control Outputs The control outputs of the 82C88 are Data Enable (DEN), Data Transmit/Receive (DT/R) and Master Cascade Enable/ Peripheral Data Enable (MCE/PDEN). The DEN signal determines when the external bus should be enabled onto the local bus and the DT/R determines the direction of data AMWC 8 O ADVANCED MEMORY WRITE COMMAND: The AMWC issues a memory write command earlier in the machine cycle to give memory devices an early indication of a write instruction. Its timing is the same as a read command signal. AMWC is active LOW. MWTC 9 O MEMORY WRITE COMMAND: This command line instructs the memory to record the data present on the data bus. This signal is active LOW. MRDC 7 O MEMORY READ COMMAND: This command line instructs the memory to drive its data onto the data bus. MRDC is active LOW. INTA 14 O INTERRUPT ACKNOWLEDGE: This command line tells an interrupting device that its interrupt has been acknowledged and that it should drive vectoring information onto the data bus. This signal is active LOW. MCE/PDEN 17 O This is a dual function pin. MCE (IOB IS TIED LOW) Master Cascade Enable occurs during an interrupt sequence and serves to read a Cascade Address from a master 82C59A Priority Interrupt Controller onto the data bus. The MCE signal is active HIGH. PDEN (IOB IS TIED HIGH): Peripheral Data Enable enables the data bus transceiver for the I/O bus that DEN performs for the system bus. PDEN is active LOW. Pin Description (Continued) PIN SYMBOL NUMBER TYPE DESCRIPTION TABLE 1. COMMAND DECODE DEFINITION S2 S1 S0 PROCESSOR STATE 82C88 COMMAND 0 0 0 Interrupt Acknowledge INTA 0 0 1 Read I/O Port IORC 0 1 0 Write I/O Port IOWC, AIOWC 0 1 1 Halt None 1 0 0 Code Access MRDC 1 0 1 Read Memory MRDC 1 1 0 Write Memory MWTC, AMWC 111 Passive None |
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