
PIC16C925/926
DS39544A-page 72
Preliminary
2001 Microchip Technology Inc.
9.3.2
MASTER MODE
Master mode of operation is supported, in firmware,
using interrupt generation on the detection of the
START and STOP conditions. The STOP (P) and
START (S) bits are cleared from a RESET, or when the
SSP module is disabled. The STOP and START bits
will toggle based on the START and STOP conditions.
Control of the I2C bus may be taken when the P bit is
set, or the bus is idle with both the S and P bits clear.
In Master mode, the SCL and SDA lines are manipu-
lated by clearing the corresponding TRISC<4:3> bit(s).
The output level is always low, irrespective of the
value(s) in PORTC<4:3>. So when transmitting data, a
’1’ data bit must have the TRISC<4> bit set (input) and
a ’0’ data bit must have the TRISC<4> bit cleared (out-
put). The same scenario is true for the SCL line with the
TRISC<3> bit.
The following events will cause SSP Interrupt Flag bit,
SSPIF, to be set (SSP Interrupt if enabled):
START condition
STOP condition
Data transfer byte transmitted/received
Master mode of operation can be done with either the
Slave mode idle (SSPM3:SSPM0 = 1011), or with the
slave active. When both Master and Slave modes are
enabled, the software needs to differentiate the
source(s) of the interrupt.
9.3.3
MULTI-MASTER MODE
In Multi-Master mode, the interrupt generation on the
detection of the START and STOP conditions allows
the determination of when the bus is free. The STOP
(P) and START (S) bits are cleared from a RESET or
when the SSP module is disabled. The STOP and
START bits will toggle based on the START and STOP
conditions. Control of the I2C bus may be taken when
bit P (SSPSTAT<4>) is set, or the bus is idle, with both
the S and P bits clear. When the bus is busy, enabling
the SSP interrupt will generate the interrupt when the
STOP condition occurs.
In multi-master operation, the SDA line must be moni-
tored to see if the signal level is the expected output
level. This check only needs to be done when a high
level is output. If a high level is expected and a low level
is present, the device needs to release the SDA and
SCL lines (set TRISC<4:3>). There are two stages
where this arbitration can be lost, they are:
Address Transfer
Data Transfer
When the slave logic is enabled, the slave continues to
receive. If arbitration was lost during the address trans-
fer stage, communication to the device may be in
progress. If addressed, an ACK pulse will be gener-
ated. If arbitration was lost during the data transfer
stage, the device will need to re-transfer the data at a
later time.
TABLE 9-4:
REGISTERS ASSOCIATED WITH I2C OPERATION
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Value on
Power-on
Reset
Value on all
other
RESETS
0Bh, 8Bh,
10Bh, 18Bh
INTCON
GIE
PEIE
TMR0IE
INTE
RBIE
TMR0IF
INTF
RBIF
0000 000x
0000 000u
0Ch
PIR1
LCDIF
ADIF
—
SSPIF
CCP1IF TMR2IF TMR1IF
00-- 0000
8Ch
PIE1
LCDIE
ADIE
—
SSPIE
CCP1IE TMR2IE TMR1IE
00-- 0000
13h
SSPBUF
Synchronous Serial Port Receive Buffer/Transmit Register
xxxx xxxx
uuuu uuuu
93h
SSPADD
Synchronous Serial Port (I2C mode) Address Register
0000 0000
14h
SSPCON
WCOL
SSPOV
SSPEN
CKP
SSPM3 SSPM2
SSPM1
SSPM0
0000 0000
94h
SSPSTAT
SMP
CKE
D/A
PS
R/W
UA
BF
0000 0000
87h
TRISC
—
PORTC Data Direction Control Register
--11 1111
Legend:
x
= unknown, u = unchanged, - = unimplemented, read as '0'. Shaded cells are not used by SSP in I2C mode.