Kawasaki 80C152, KS152JB, 80C51 technical specifications Baud Rate

KS152JB Universal Communications Controller Technical Specifications

this same DMA bit.

The interrupts EGSTE (IEN1.5), GSC transmit error; EGSTV (IEN1.3), GSC transmit valid; EGSRE (IEN1.1), GSC receive error; and EGSRV (IEN1.0), GSC receive valid; need to be enabled. The DMA interrupts are normally not used when servicing the GSC with the DMA chan- nels. To ensure that the DMA interrupts are normally not used when servicing the GSC with the DMA channels. To ensure that the DMA interrupts are not responded to is a function of the user software and should be checked by the software to make sure they are not enabled. priority for these interrupts can also be set at this time. Whether to use high or low priority needs to be decided by the user. When responding to the GSC interrupts, if a buffer is being used to store the GSC information, then the DMA registers used for the buffer will probably need updating.

After this initialization, all that needs to be done when the GSC is actually going to be used is: load the byte count, set-up the source addresses for the DMA channel servicing the transmitter, set-up the destination addresses for the DMA channel servicing the receiver, and start the DMA transfer. The GSC enable bits should be set first and then the GO bits for the DMA. This initiates the data transfers.

This simplifies the maintenance of the GSC and can make the implementation of an external buffer for packetized information automatic.

An external buffer can be used as the source of data for transmission, or the destination of data from the receiver. In this arrangement, the message size is limited to the RAM size or 64K, which- ever is smaller. By using an external buffer, the data can be accessed by other devices which may want access to the serial data. The amount of time required for the external data moves will also decrease. Under CPU control, a “MOVX” command would take 24 oscillator periods to complete.

Under DMA control, external to internal, or internal to external, data moves take only 12 oscilla- tor periods.

3.5.4 BAUD RATE

The GSC baud rate is determined by the contents of the SFR, BAUD, or the external clock. The formula used to determine the baud rate when using the internal clock is:

(fosc)/ ((BAUD +1)*8)

For example if a 12 MHz oscillator is used the baud rate can vary from:

12,000,000/ ((0+1)*8) = 1.5 MBPS

to:

12,000,000/((255+1)*8) = 5.859 KBPS

There are certain requirements that the external clock will need to meet. These requirements are

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