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BBC Micro Elite

Market: TT219

Name: TT219 [View in context] Type: Subroutine Category: Market Summary: Show the Buy Cargo screen (red key f1)
Other entry points: BAY2 Jump into the main loop at FRCE, setting the key "pressed" to red key f9 (so we show the Inventory screen)
.TT219 \LDA#2 \ This instruction is commented out in the original \ source. Perhaps this view originally had a QQ11 value \ of 2, but it turned out not to need its own unique ID, \ so the authors found they could just use a view value \ of 1 and save an instruction at the same time? JSR TT66-2 \ Clear the top part of the screen, draw a white border, \ and set the current view type in QQ11 to 1 JSR TT163 \ Print the column headers for the prices table LDA #%10000000 \ Set bit 7 of QQ17 to switch to Sentence Case, with the STA QQ17 \ next letter in capitals \JSR FLKB \ This instruction is commented out in the original \ source. It calls a routine to flush the keyboard \ buffer (FLKB) that isn't present in the cassette \ version but is in the disc version LDA #0 \ We're going to loop through all the available market STA QQ29 \ items, so we set up a counter in QQ29 to denote the \ current item and start it at 0 .TT220 JSR TT151 \ Call TT151 to print the item name, market price and \ availability of the current item, and set QQ24 to the \ item's price / 4, QQ25 to the quantity available and \ QQ19+1 to byte #1 from the market prices table for \ this item LDA QQ25 \ If there are some of the current item available, jump BNE TT224 \ to TT224 below to see if we want to buy any JMP TT222 \ Otherwise there are none available, so jump down to \ TT222 to skip this item .TQ4 LDY #176 \ Set Y to the recursive token 16 ("QUANTITY") .Tc JSR TT162 \ Print a space TYA \ Print the recursive token in Y followed by a question JSR prq \ mark .TTX224 JSR dn2 \ Call dn2 to make a short, high beep and delay for 1 \ second .TT224 JSR CLYNS \ Clear the bottom three text rows of the upper screen, \ and move the text cursor to column 1 on row 21, i.e. \ the start of the top row of the three bottom rows LDA #204 \ Print recursive token 44 ("QUANTITY OF ") JSR TT27 LDA QQ29 \ Print recursive token 48 + QQ29, which will be in the CLC \ range 48 ("FOOD") to 64 ("ALIEN ITEMS"), so this ADC #208 \ prints the current item's name JSR TT27 LDA #'/' \ Print "/" JSR TT27 JSR TT152 \ Print the unit ("t", "kg" or "g") for the current item \ (as the call to TT151 above set QQ19+1 with the \ appropriate value) LDA #'?' \ Print "?" JSR TT27 JSR TT67 \ Print a newline LDX #0 \ These instructions have no effect, as they are STX R \ repeated at the start of gnum, which we call next. LDX #12 \ Perhaps they were left behind when code was moved from STX T1 \ here into gnum, and weren't deleted? \.TT223 \ This label is commented out in the original source, \ and is a duplicate of a label in gnum, so this could \ also be a remnant if the code in gnum was originally \ here, but got moved into the gnum subroutine JSR gnum \ Call gnum to get a number from the keyboard, which \ will be the quantity of this item we want to purchase, \ returning the number entered in A and R BCS TQ4 \ If gnum set the C flag, the number entered is greater \ then the quantity available, so jump up to TQ4 to \ display a "Quantity?" error, beep, clear the number \ and try again STA P \ Otherwise we have a valid purchase quantity entered, \ so store the amount we want to purchase in P JSR tnpr \ Call tnpr to work out whether there is room in the \ cargo hold for this item LDY #206 \ If the C flag is set, then there is no room in the BCS Tc \ cargo hold, so set Y to the recursive token 46 \ (" CARGO{switch to sentence case}") and jump up to \ Tc to print a "Cargo?" error, beep, clear the number \ and try again LDA QQ24 \ There is room in the cargo hold, so now to check STA Q \ whether we have enough cash, so fetch the item's \ price / 4, which was returned in QQ24 by the call \ to TT151 above and store it in Q JSR GCASH \ Call GCASH to calculate \ \ (Y X) = P * Q * 4 \ \ which will be the total price of this transaction \ (as P contains the purchase quantity and Q contains \ the item's price / 4) JSR LCASH \ Subtract (Y X) cash from the cash pot in CASH LDY #197 \ If the C flag is clear, we didn't have enough cash, BCC Tc \ so set Y to the recursive token 37 ("CASH") and jump \ up to Tc to print a "Cash?" error, beep, clear the \ number and try again LDY QQ29 \ Fetch the current market item number from QQ29 into Y LDA R \ Set A to the number of items we just purchased (this \ was set by gnum above) PHA \ Store the quantity just purchased on the stack CLC \ Add the number purchased to the Y-th byte of QQ20, ADC QQ20,Y \ which contains the number of items of this type in STA QQ20,Y \ our hold (so this transfers the bought items into our \ cargo hold) LDA AVL,Y \ Subtract the number of items from the Y-th byte of SEC \ AVL, which contains the number of items of this type SBC R \ that are available on the market STA AVL,Y PLA \ Restore the quantity just purchased BEQ TT222 \ If we didn't buy anything, jump to TT222 to skip the \ following instruction JSR dn \ Call dn to print the amount of cash left in the cash \ pot, then make a short, high beep to confirm the \ purchase, and delay for 1 second .TT222 LDA QQ29 \ Move the text cursor to row QQ29 + 5 (where QQ29 is CLC \ the item number, starting from 0) ADC #5 STA YC LDA #0 \ Move the text cursor to column 0 STA XC INC QQ29 \ Increment QQ29 to point to the next item LDA QQ29 \ If QQ29 >= 17 then jump to BAY2 as we have done the CMP #17 \ last item BCS BAY2 JMP TT220 \ Otherwise loop back to TT220 to print the next market \ item .BAY2 LDA #f9 \ Jump into the main loop at FRCE, setting the key JMP FRCE \ "pressed" to red key f9 (so we show the Inventory \ screen)