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MAH3690CD Datasheet(PDF) 5 Page - Dynex Semiconductor |
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MAH3690CD Datasheet(HTML) 5 Page - Dynex Semiconductor |
5 / 41 page MA3690/1/3 5/41 Four bits of the Instruction word (bits 10-7) define conditions under which the terminal will generate an interrupt to the subsystem (IRQN). Note that the generation of IRQN will only take place after any selected retry conditions have been exhausted. The interrupt conditions which may be selected can be categorised as follows: 1. Interrupt if no response - the terminal will generate an interrupt if the RT does not respond. 2. Interrupt if Status bit set - the terminal will generate an interrupt if a received status word has a bit set other than in the RT address field or if the wrong RT responds. 3. Interrupt Always - the terminal will generate an interrupt regardless of whether the message was successful or not. 4. Interrupt if word error - the terminal will generate an interrupt if a word encoding or word count error occurs. In all of the above cases, the terminal will generate a 250ns pulse on IRQN and enter the halted state. This will occur after the Report sequence has been executed. Note the INCADRN will not be produced. Retry Condition Code Definition 001 Retry if error 010 Retry if status bit set 100 Retry if busy set Three bits of the Instruction word (bits 13-11) are used as flags to specify conditions under which the terminal will execute automatic message retries until the retry number count is zero. The retry flags are involved with the following conditions: 1. Retry if error - this includes a no-status response, a word encoding error, or a wrong word count from a responding RT. 2. Retry if Status bit set - an automatic retry will take place if a received status word has a bit set, other than in the RT address field, or if the wrong RT responds. 3. Retry if Busy - this is a specific check for the setting of the Busy bit in a responding RT’s status word. The remaining two bits of the Instruction word specify the number of message retries which the Bus Controller will attempt automatically. A code of 00 specifies no retries, a code of 11 specifies the maximum of three retries. The retries are in addition to the initial message transmitted, hence a message may be transmitted four times in total, if not successful. Note that if the condition which is being tested becomes invalid, the retry sequence will discontinue on the next message with the Bus Controller completing execution of the message in the relevant manner. Retry Count The two most significant bits of the instruction word specify the number of retries to be carried out when a retry condition has been detected. (Maximun 3 given by code 11) RECEIVE COMMAND WORD The receive command word is addressed when CODENN and C1 are both low and R/WN and C0 are both high. This word is the command word which will be transmitted for a BC to RT transfer or as the first command word of an RT to RT transfer. Note: This word should be set to 1111 HEX if the message code is 000 or 100, or if the Function Code is not 00. TRANSMIT COMMAND WORD The transmit command word is addressed when CODENN and C0 are both low and R/WN and C1 are both high. This word is the command word which will be transmitted for an RT to BC transfer or as the second command word of an RT to RT transfer. Note: This word should be set to 1111 HEX if the message code is 001 or 101, or if the Function Code is not 00. DATA POINTER WORD The data pointer word is addressed when CODENN is low and C0, C1 and R/WN are all high. This word is intended as a base address pointer to the subsystem data store thus specifying where any data words associated with the current instruction should be stored or retrieved from. As such, this word is not read into the terminal itself but is merely transferred from the Instruction Store to a suitable external address latch. (The BUFENN signal is therefore inactive during this transfer). |
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