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SC68C652BIB48 Datasheet(PDF) 10 Page - NXP Semiconductors |
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SC68C652BIB48 Datasheet(HTML) 10 Page - NXP Semiconductors |
10 / 43 page SC68C652B_2 © NXP B.V. 2009. All rights reserved. Product data sheet Rev. 02 — 2 November 2009 10 of 43 NXP Semiconductors SC68C652B Dual UART with 32-byte FIFOs and IrDA encoder/decoder 6.4 Hardware flow control When automatic hardware flow control is enabled, the SC68C652B monitors the CTSn pin for a remote buffer overflow indication and controls the RTSn pin for local buffer overflows. Automatic hardware flow control is selected by setting EFR[6] (RTS) and EFR[7] (CTS) to a logic 1. If CTSn transitions from a logic 0 to a logic 1 indicating a flow control request, ISR[5] will be set to a logic 1 (if enabled via IER[6:7]), and the SC68C652B will suspend TXn transmissions as soon as the stop bit of the character in process is shifted out. Transmission is resumed after the CTSn input returns to a logic 0, indicating more data may be sent. With the auto-RTS function enabled, an interrupt is generated when the receive FIFO reaches the programmed trigger level. The RTSn pin will not be forced to a logic 1 (RTS off), until the receive FIFO reaches the next trigger level. However, the RTSn pin will return to a logic 0 after the data buffer (FIFO) is unloaded to the next trigger level below the programmed trigger level. However, under the above described conditions, the SC68C652B will continue to accept data until the receive FIFO is full. 6.5 Software flow control When software flow control is enabled, the SC68C652B compares one or two sequential receive data characters with the programmed Xon or Xoff character value(s). If received character(s) match the programmed Xoff values, the SC68C652B will halt transmission as soon as the current character(s) has completed transmission. When a match occurs, the receive ready (if enabled via Xoff IER[5]) flags will be set and the interrupt output pin (if receive interrupt is enabled) will be activated. Following a suspension due to a match of the Xoff characters’ values, the SC68C652B will monitor the receive data stream for a match to the Xon1/Xon2 character value(s). If a match is found, the SC68C652B will resume operation and clear the flags (ISR[4]). Reset initially sets the contents of the Xon/Xoff 8-bit flow control registers to a logic 0. Following reset, the user can write any Xon/Xoff value desired for software flow control. Different conditions can be set to detect Xon/Xoff characters and suspend/resume transmissions. When double 8-bit Xon/Xoff characters are selected, the SC68C652B compares two consecutive receive characters with two software flow control 8-bit values (Xon1, Xon2, Xoff1, Xoff2) and controls TXn transmissions accordingly. Under the above described flow control mechanisms, flow control characters are not placed (stacked) in the user accessible receive data buffer or FIFO. When using a software flow control, the Xon/Xoff characters cannot be used for data transfer. In the event that the receive buffer is overfilling and flow control needs to be executed, the SC68C652B automatically sends an Xoff message (when enabled) via the serial TXn output to the remote modem. The SC68C652B sends the Xoff1/Xoff2 characters as soon Table 5. Flow control mechanism Selected trigger level (characters) IRQ pin activation Negate RTS or send Xoff Assert RTS or send Xon RX TX 88 16 8 0 16 16 8 16 7 24 24 24 24 15 28 28 30 28 23 |
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