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ST16C454 Datasheet(PDF) 12 Page - Exar Corporation |
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ST16C454 Datasheet(HTML) 12 Page - Exar Corporation |
12 / 29 page ST16C454 12 Rev. 3.31 Loop-back Mode The internal loop-back capability allows onboard diag- nostics. In the loop-back mode the normal modem interface pins are disconnected and reconfigured for loop-back internally. MCR register bits 0-3 are used for controlling loop-back diagnostic testing. In the loop- back mode OP1 and OP2 in the MCR register (bits 3/ 2) control the modem -RI and -CD inputs respectively. MCR signals -DTR and -RTS (bits 0-1) are used to control the modem -CTS and -DSR inputs respectively. The transmitter output (TX) and the receiver input (RX) are disconnected from their associated interface pins, and instead are connected together internally (See Figure 12). The -CTS, -DSR, -CD, and -RI are discon- nected from their normal modem control inputs pins, and instead are connected internally to -DTR, -RTS, - OP1 and -OP2. Loop-back test data is entered into the transmit holding register via the user data bus interface, D0-D7. The transmit UART serializes the data and passes the serial data to the receive UART via the internal loop-back connection. The receive UART con- verts the serial data back into parallel data that is then made available at the user data interface, D0-D7. The user optionally compares the received data to the initial transmitted data for verifying error free operation of the UART TX/RX circuits. In this mode, the receiver and transmitter interrupts are fully operational. The Modem Control Interrupts are also operational. However, the interrupts can only be read using lower four bits of the Modem Control Register (MCR bits 0-3) instead of the four Modem Status Register bits 4-7. The interrupts are still con- trolled by the IER. C1 22pF C2 33pF X1 1.8432 MHz Figure 8, Crystal oscillator connection |
Similar Part No. - ST16C454_05 |
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Similar Description - ST16C454_05 |
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