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Page 11



4.2 Transmitter Operation

The transmitter section accepts parallel data, formats it, and transmits it in serial form (Figure 5) on the TRO terminal.. D4  to D7 are not used as the input number formatted to a nibble thus using 4 LSBs.

Fig. 5 Illustration of bit format of Transmit bit format


Transmitter timing is shown in Figure 6. (A) Data is loaded into the transmitter buffer register from the inputs TBR1 through TBR4 by a logic low on the TBRL input. Valid data must be present at least tDT prior to, and  tTD  following, the rising edge of TBRL. Since 4-bits are used, only the least significant bits are used. The character is right justi-fied into the least significant bit, TBR1. (B) The rising edge of TBRL clears TBRE. 1/2 to 11/2 cycles later, depending on when the TBRL pulse occurs with respect to TRC, data is transferred to the transmitter register and TRE is cleared. TBRE is set to a logic High one cycle after that.

Output data is clocked by TRC. The clock rate is 16 times the data rate. (C) A second pulse on TBRL loads data  into the transmitter buffer register. Data transfer to the transmitter register is delayed until transmission of the current character is complete. (D) Data is automatically transferred to the transmitter register and transmission of that character begins.


Fig. 6 Transmitter timing diagram





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Last modified: July 13, 2002