PIC17C7XX Datasheet, PDF (142/328 Pages) Microchip Technology – High-Performance 8-Bit CMOS EPROM Microcontrollers with 10-bit A/D

PIC17C7XX
The SSPSTAT register gives the status of the data
transfer. This information includes detection of a
START or STOP bit, specifies if the received byte was
data or address if the next byte is the completion of
10-bit address, and if this will be a read or write data
transfer.
The SSPBUF is the register to which transfer data is
written to or read from. The SSPSR register shifts the
data in or out of the device. In receive operations, the
SSPBUF and SSPSR create a doubled buffered
receiver. This allows reception of the next byte to begin
before reading the last byte of received data. When the
complete byte is received, it is transferred to the
SSPBUF register and flag bit SSPIF is set. If another
complete byte is received before the SSPBUF register
is read, a receiver overflow has occurred and bit
SSPOV (SSPCON1<6>) is set and the byte in the
SSPSR is lost.
The SSPADD register holds the slave address. In 10-bit
mode, the user needs to write the high byte of the
address (1111 0 A9 A8 0). Following the high byte
address match, the low byte of the address needs to be
loaded (A7:A0).
15.2.1 SLAVE MODE
In slave mode, the SCL and SDA pins must be config-
ured as inputs. The MSSP module will override the
input state with the output data when required
(slave-transmitter).
When an address is matched or the data transfer after
an address match is received, the hardware automati-
cally will generate the acknowledge (ACK) pulse, and
then load the SSPBUF register with the received value
currently in the SSPSR register.
There are certain conditions that will cause the MSSP
module not to give this ACK pulse. These are if either
(or both):
a) The buffer full bit BF (SSPSTAT<0>) was set
before the transfer was received.
b) The overflow bit SSPOV (SSPCON1<6>) was
set before the transfer was received.
If the BF bit is set, the SSPSR register value is not
loaded into the SSPBUF, but bit SSPIF and SSPOV are
set. Table 15-2 shows what happens when a data
transfer byte is received, given the status of bits BF and
SSPOV. The shaded cells show the condition where
user software did not properly clear the overflow condi-
tion. Flag bit BF is cleared by reading the SSPBUF reg-
ister while bit SSPOV is cleared through software.
The SCL clock input must have a minimum high and
low time for proper operation. The high and low times
of the I²C specification as well as the requirement of the
MSSP module is shown in timing parameter #100 and
parameter #101 of the Electrical Specifications.
DS30289A-page 142
© 1998 Microchip Technology Inc.