SLAU144K December 2004 – August 2022 MSP430AFE221 , MSP430AFE222 , MSP430AFE223 , MSP430AFE231 , MSP430AFE232 , MSP430AFE233 , MSP430AFE251 , MSP430AFE252 , MSP430AFE253 , MSP430F2001 , MSP430F2002 , MSP430F2003 , MSP430F2011 , MSP430F2012 , MSP430F2013 , MSP430F2101 , MSP430F2111 , MSP430F2112 , MSP430F2121 , MSP430F2122 , MSP430F2131 , MSP430F2132 , MSP430F2132-EP , MSP430F2232 , MSP430F2234 , MSP430F2252 , MSP430F2252-Q1 , MSP430F2254 , MSP430F2272 , MSP430F2272-Q1 , MSP430F2274 , MSP430F2274-EP , MSP430F233 , MSP430F2330 , MSP430F235 , MSP430F2350 , MSP430F2370 , MSP430F2410 , MSP430F2416 , MSP430F2417 , MSP430F2418 , MSP430F2419 , MSP430F247 , MSP430F2471 , MSP430F248 , MSP430F2481 , MSP430F249 , MSP430F2491 , MSP430F2616 , MSP430F2617 , MSP430F2618 , MSP430F2619 , MSP430G2001 , MSP430G2101 , MSP430G2102 , MSP430G2111 , MSP430G2112 , MSP430G2121 , MSP430G2131 , MSP430G2132 , MSP430G2152 , MSP430G2153 , MSP430G2201 , MSP430G2201-Q1 , MSP430G2202 , MSP430G2203 , MSP430G2210 , MSP430G2211 , MSP430G2212 , MSP430G2213 , MSP430G2221 , MSP430G2230 , MSP430G2231 , MSP430G2231-Q1 , MSP430G2232 , MSP430G2233 , MSP430G2252 , MSP430G2253 , MSP430G2302 , MSP430G2303 , MSP430G2312 , MSP430G2313 , MSP430G2332 , MSP430G2333 , MSP430G2352 , MSP430G2353 , MSP430G2402 , MSP430G2403 , MSP430G2412 , MSP430G2413 , MSP430G2432 , MSP430G2433 , MSP430G2444 , MSP430G2452 , MSP430G2453 , MSP430G2513 , MSP430G2533 , MSP430G2544 , MSP430G2553 , MSP430G2744 , MSP430G2755 , MSP430G2855 , MSP430G2955 , MSP430TCH5E
In I2C receiver mode the output must be disabled by clearing USIOE and the USI module is prepared for reception by writing 8 into USICNTx. This clears USIIFG and SCL is generated in master mode or released from being held low in slave mode. The USIIFG bit will be set after 8 clocks. This stops the clock signal on SCL in master mode or holds SCL low at the next low phase in slave mode.
To transmit an acknowledge or no-acknowledge bit, the MSB of the shift register is loaded with 0 or 1, the USIOE bit is set with software to enable the output, and 1 is written to the USICNTx bits. As soon as the MSB bit is shifted out, USIIFG will be become set and the module can be prepared for the reception of the next I2C data byte.
; Generate ACK
BIS.B #USIOE,&USICTL0 ; SDA output
MOV.B #00h,&USISRL ; MSB = 0
MOV.B #01h,&USICNT ; USICNTx = 1
TEST_USIIFG
BIT.B #USIIFG,&USICTL1 ; Test USIIFG
JZ TEST_USIIFG
...continue...
; Generate NACK
BIS.B #USIOE,&USICTL0 ; SDA output
MOV.B #0FFh,&USISRL ; MSB = 1
MOV.B #01h,&USICNT ; USICNTx = 1
TEST_USIIFG
BIT.B #USIIFG,&USICTL1 ; Test USIIFG
JZ TEST_USIIFG
...continue...