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4e-onewire.s43
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4e-onewire.s43
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;****h* 4e4th/4e-onewire
; NAME
; 4e-onewire
; SYNOPSIS
; Dallas 1-wire drivers for 4e4th/CamelForth.
; DESCRIPTION
; These are "bit-banging" 1-wire drivers for the MSP430G2553
; MCU installed on a TI Launchpad board.
; Currently configured to use P2.3, with MCLK=8 MHz.
; NOTES
; 4e4th configures MCLK = DCOCLK = 8 MHz (see 4e-init430G2553.s43).
; Launchpad I/O pin usage:
; P1.0 - LED1 output
; P1.1 - UART
; P1.2 - UART
; P1.3 - SW2 input (internal pullup enabled)
; P1.4 - output (configured by 4e4th)
; P1.5 - output (configured by 4e4th)
; P2.0
; P2.1
; P2.2
; P2.3 - 1-wire I/O
; P2.4
; P2.5
; P1.6 - LED2 output
; P1.7
; MSP430G2553 pins are capable of sourcing or sinking 6 mA.
; Internal pullup resistor is 20-50 Kohm, typ. 35 Kohm, which
; is too high, so an external pullup resistor is required.
; Dallas DS18B20 data sheet suggests 4.7 Kohm pullup resistor.
; Dallas App Note 132 suggests 1.1 Kohm pullup resistor.
; Either external pullup is within limits for drive current.
;
; Note that the MSP430 does not have open-drain outputs.
; To simulate open-drain, a "0" is written to the pin's output
; register. When a "1" is written to the pin's direction register,
; the output is enabled and "0" is output. When a "0" is written
; to the direction register, the input is enabled and the pin is
; Hi-Z (equivalent to an open-drain "1" output).
; HISTORY
; 23 nov 12 bjr - Changed to use P2.3 for 1-wire I/O.
; 19 nov 12 bjr - Refactored code to make OWSLOT primitive instead
; of OWTOUCH.
; 23 oct 12 bjr - Created.
; AUTHOR
; B. J. Rodriguez
; COPYRIGHT
; (c) 2012 Bradford J. Rodriguez.
;
; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation; either version 3 of the License, or
; (at your option) any later version.
;
; This program is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program. If not, see <http://www.gnu.org/licenses/>.
;
; Commercial inquiries should be directed to the author at
; 115 First St., #105, Collingwood, Ontario L9Y 4W3 Canada
; or via email to bj@camelforth.com
;******
; define port registers and pin to be used for 1-wire (P2.3)
#define OWIN P2IN
#define OWOUT P2OUT
#define OWDIR P2DIR
#define OWREN P2REN
#define OWBIT BIT3
; define MCLK frequency in MHz.
MCLK EQU 8
; Define a software delay of N usec for our MCLK freq (8 MHz)
; Uses scratch register X.
; Note that due to truncation, may delay as many as 2 MCLK cycles
; short of the specified period. For 1-wire code this is ok,
; since we always have other instructions using at least 2 cycles.
DELAY MACRO usec
LOCAL loop
MOV #(((usec*MCLK)-2)/3),X ; 2
loop: SUB #1,X ; 1n
JNZ loop ; 2n
ENDM
;****f* 4e-onewire/OWRESET
; NAME
; OWRESET
; SYNOPSIS
; OWRESET ( -- f ) Initialize 1-wire devices; return true if present
; DESCRIPTION
; This configures the port pin used by the 1-wire interface, and then
; sends an "initialize" sequence to the 1-wire devices. If any device
; is present, it will be detected.
;
; Timing, per DS18B20 data sheet:
; a) Output "0" (drive output low) for >480 usec.
; b) Output "1" (let output float).
; c) After 15 to 60 usec, device will drive pin low for 60 to 240 usec.
; So, wait 75 usec and sample input.
; d) Leave output high (floating) for at least 480 usec.
;******
HEADER OWRESET,7,'OWRESET',DOCODE
; push old TOS onto stack
SUB #2,PSP ; 1
MOV TOS,0(PSP) ; 4
; preclear result in TOS
MOV #0,TOS
; initialize the pin used for the 1-wire.
BIC.B #OWBIT,OWDIR ; make pin an input
BIC.B #OWBIT,OWOUT ; make output bit a "0"
BIC.B #OWBIT,OWREN ; disable internal pullup
; Delay >480 usec in case output pin had been low
DELAY 500
; Pull output low
BIS.B #OWBIT,OWDIR ; make pin output, sends "0"
; Delay >480 usec
DELAY 500
; Critical timing period, disable interrupts.
BIC #8,SR ; clear GIE bit
; Pull output high
BIC.B #OWBIT,OWDIR ; make pin input, sends "1"
; Delay 75 usec
DELAY 75
; Sample input pin, set TOS if input is zero
BIT.B #OWBIT,OWIN
JNZ OWNONE
MOV #-1,TOS ; if input zero, an 1-wire is present
OWNONE:
; End critical timing period, enable interrupts
BIS #8,SR ; set GIE bit
; Delay rest of 480 usec (we've already delayed 75 usec)
DELAY 405
; we now have the result flag in TOS
NEXT
;****f* 4e-onewire/OWSLOT
; NAME
; OWSLOT
; SYNOPSIS
; OWSLOT ( c -- c' ) Write and read one bit to/from 1-wire.
; DESCRIPTION
; The "touch byte" function is described in Dallas App Note 74.
; It outputs a byte to the 1-wire pin, LSB first, and reads back
; the state of the 1-wire pin after a suitable delay.
; To read a byte, output $FF and read the reply data.
; To write a byte, output that byte and discard the reply.
;
; This function performs one bit of the "touch" operation --
; one read/write "slot" in Dallas jargon. Perform this eight
; times in a row to get the "touch byte" function.
;
; PARAMETERS
; The input parameter is xxxxxxxxbbbbbbbo where
; 'xxxxxxxx' are don't cares,
; 'bbbbbbb' are bits to be shifted down, and
; 'o' is the bit to be output in the slot. This must be 1
; to create a read slot.
;
; The returned value is xxxxxxxxibbbbbbb where
; 'xxxxxxxx' are not known (the input shifted down 1 position),
; 'i' is the bit read during the slot. This has no meaning
; if it was a write slot.
; 'bbbbbbb' are the 7 input bits, shifted down one position.
;
; This peculiar parameter usage allows OWTOUCH to be written as
; OWSLOT OWSLOT OWSLOT OWSLOT OWSLOT OWSLOT OWSLOT OWSLOT
;
; NOTES
; Interrupts are disabled during each bit.
; Timing, per DS18B20 data sheet:
; a) Output "0" for start period. (> 1 us, < 15 us, typ. 6 us*)
; b) Output data bit (0 or 1), open drain
; c) After MS from start of cycle, sample input (15 to 60 us, typ. 25 us*)
; d) After write-0 period from start of cycle, output "1" (>60 us)
; e) After recovery period, loop or return. (> 1 us)
; For writes, DS18B20 samples input 15 to 60 usec from start of cycle.
; * "Typical" values are per App Note 132 for a 300m cable length.
; --------- -------------------------------
; \ / /
; -------------------------------
; a b c d e
; | 6us | 19us | 35us | 2us |
;******
HEADER OWSLOT,6,'OWSLOT',DOCODE
BIC #0x100,TOS ; preclear result bit in TOS
; disable interrupts
BIC #8,SR ; clear GIE bit
; output a "0"
BIS.B #OWBIT,OWDIR ; make pin output, sends "0"
BIC.B #OWBIT,OWOUT ; just in case, ensure 0 is output
; delay 6 usec
DELAY 6
; output the LSB (no action required if LSB=0)
BIT #1,TOS
JZ OWSEND0
BIC.B #OWBIT,OWDIR ; make pin input, sends "1"
OWSEND0:
; delay 19 usec
DELAY 19
; sample the input (no action required if zero)
BIT.B #OWBIT,OWIN
JZ OWRECV0
BIS #0x100,TOS ; if input=1, store 1 in high TOS
OWRECV0: RRA TOS ; shift TOS down 1 bit
; delay 35 usec
DELAY 35
; output a "1"
BIC.B #OWBIT,OWDIR ; make pin input = Hi-Z
; enable interrupts
BIS #8,SR ; set GIE bit
; delay 2 usec
DELAY 2
; note that NEXT will take 0.5 usec (4 clocks)
; we now have the received bit in the 0x80 bit of TOS.
NEXT