diff options
Diffstat (limited to 'src/emu/machine/74148.c')
-rw-r--r-- | src/emu/machine/74148.c | 193 |
1 files changed, 193 insertions, 0 deletions
diff --git a/src/emu/machine/74148.c b/src/emu/machine/74148.c new file mode 100644 index 00000000000..d7eae2e7f53 --- /dev/null +++ b/src/emu/machine/74148.c @@ -0,0 +1,193 @@ +/***************************************************************************** + + 74148 8-line-to-3-line priority encoder + + + Pin layout and functions to access pins: + + input_line_w(4) [1] /IN4 VCC [16] + input_line_w(5) [2] /IN5 /EO [15] enable_output_r + input_line_w(6) [3] /IN6 /GS [14] output_valid_r + input_line_w(7) [4] /IN7 /IN3 [13] input_line_w(3) + enable_input_w [5] /EI /IN2 [12] input_line_w(2) + output_r [6] /A2 /IN1 [11] input_line_w(1) + output_r [7] /A1 /IN0 [10] input_line_w(0) + [8] GND /A0 [9] output_r + + + Truth table (all logic levels indicate the actual voltage on the line): + + INPUTS | OUTPUTS + | + EI I0 I1 I2 I3 I4 I5 I6 I7 | A2 A1 A0 | GS EO + ----------------------------+----------+------ + 1 H X X X X X X X X | H H H | H H + 2 L H H H H H H H H | H H H | H L + 3 L X X X X X X X L | L L L | L H + 4 L X X X X X X L H | L L H | L H + 5 L X X X X X L H H | L H L | L H + 6 L X X X X L H H H | L H H | L H + 7 L X X X L H H H H | H L L | L H + 8 L X X L H H H H H | H L H | L H + 9 L X L H H H H H H | H H L | L H + 10 L L H H H H H H H | H H H | L H + ----------------------------+----------+------ + L = lo (0) + H = hi (1) + X = any state + +*****************************************************************************/ + +#include "driver.h" +#include "machine/74148.h" + + +#define MAX_TTL74148 4 + +struct TTL74148 +{ + /* callback */ + void (*output_cb)(void); + + /* inputs */ + int input_lines[8]; /* pins 1-4,10-13 */ + int enable_input; /* pin 5 */ + + /* outputs */ + int output; /* pins 6,7,9 */ + int output_valid; /* pin 14 */ + int enable_output; /* pin 15 */ + + /* internals */ + int last_output; + int last_output_valid; + int last_enable_output; +}; + +static struct TTL74148 chips[MAX_TTL74148]; + + +void TTL74148_update(int which) +{ + if (chips[which].enable_input) + { + // row 1 in truth table + chips[which].output = 0x07; + chips[which].output_valid = 1; + chips[which].enable_output = 1; + } + else + { + int bit0, bit1, bit2; + + /* this comes straight off the data sheet schematics */ + bit0 = !((!chips[which].input_lines[1] & + chips[which].input_lines[2] & + chips[which].input_lines[4] & + chips[which].input_lines[6]) | + (!chips[which].input_lines[3] & + chips[which].input_lines[4] & + chips[which].input_lines[6]) | + (!chips[which].input_lines[5] & + chips[which].input_lines[6]) | + (!chips[which].input_lines[7])); + + bit1 = !((!chips[which].input_lines[2] & + chips[which].input_lines[4] & + chips[which].input_lines[5]) | + (!chips[which].input_lines[3] & + chips[which].input_lines[4] & + chips[which].input_lines[5]) | + (!chips[which].input_lines[6]) | + (!chips[which].input_lines[7])); + + bit2 = !((!chips[which].input_lines[4]) | + (!chips[which].input_lines[5]) | + (!chips[which].input_lines[6]) | + (!chips[which].input_lines[7])); + + chips[which].output = (bit2 << 2) | (bit1 << 1) | bit0; + + chips[which].output_valid = (chips[which].input_lines[0] & + chips[which].input_lines[1] & + chips[which].input_lines[2] & + chips[which].input_lines[3] & + chips[which].input_lines[4] & + chips[which].input_lines[5] & + chips[which].input_lines[6] & + chips[which].input_lines[7]); + + chips[which].enable_output = !chips[which].output_valid; + } + + + /* call callback if any of the outputs changed */ + if ( chips[which].output_cb && + ((chips[which].output != chips[which].last_output) || + (chips[which].output_valid != chips[which].last_output_valid) || + (chips[which].enable_output != chips[which].last_enable_output))) + { + chips[which].last_output = chips[which].output; + chips[which].last_output_valid = chips[which].output_valid; + chips[which].last_enable_output = chips[which].enable_output; + + chips[which].output_cb(); + } +} + + +void TTL74148_input_line_w(int which, int input_line, int data) +{ + chips[which].input_lines[input_line] = data ? 1 : 0; +} + + +void TTL74148_enable_input_w(int which, int data) +{ + chips[which].enable_input = data ? 1 : 0; +} + + +int TTL74148_output_r(int which) +{ + return chips[which].output; +} + + +int TTL74148_output_valid_r(int which) +{ + return chips[which].output_valid; +} + + +int TTL74148_enable_output_r(int which) +{ + return chips[which].enable_output; +} + + + +void TTL74148_config(int which, const struct TTL74148_interface *intf) +{ + if (which >= MAX_TTL74148) + { + logerror("Only %d 74148's are supported at this time.\n", MAX_TTL74148); + return; + } + + + chips[which].output_cb = (intf ? intf->output_cb : 0); + chips[which].enable_input = 1; + chips[which].input_lines[0] = 1; + chips[which].input_lines[1] = 1; + chips[which].input_lines[2] = 1; + chips[which].input_lines[3] = 1; + chips[which].input_lines[4] = 1; + chips[which].input_lines[5] = 1; + chips[which].input_lines[6] = 1; + chips[which].input_lines[7] = 1; + + chips[which].last_output = -1; + chips[which].last_output_valid = -1; + chips[which].last_enable_output = -1; +} |